Power Converter

Convert between SI and historical power units (watt, kilowatt, megawatt, mechanical horsepower, metric horsepower / PS, electric horsepower, BTU per hour, kilocalorie per hour, foot-pound per second). Disambiguates the three horsepower variants that vary by hundreds of watts.

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From

Value

Result

0.7457 kW

1 hp= 0.7457 kW

Decimals

All units

Unit	Value
Watt (W)	745.7
Kilowatt (kW)	0.7457
Megawatt (MW)	7.457E-4
Mechanical horsepower (hp)	1
Metric horsepower (PS) (PS)	1.01387
Electric horsepower (hp (E))	0.999598
BTU per hour (BTU/h)	2,544.43
Kilocalorie per hour (kcal/h)	641.616
Foot-pound per second (ft·lbf/s)	550

Three horsepower variants exist: mechanical hp (550 ft·lbf/s, US auto specs), metric hp / PS (75 kgf·m/s, EU auto specs), electric hp (746 W exact, US motor nameplates). They differ by ~10 W — never substitute one for another in engineering work.

Ažurirano: 20. svibnja 2026.

Power converter. SI, three horsepower variants, thermal and gravitational power units with NIST-exact factors.

A power converter pivots a value through the watt across 9 units in four groups (SI, horsepower, thermal, gravitational), surfacing all three horsepower variants. It disambiguates mechanical hp, metric hp (PS), and electric hp so a Porsche "510 PS" rating is not silently misread as US mechanical hp; 7 of 9 unit factors are bit-exact while BTU/h and kcal/h carry IEEE-754 drift from the per-hour denominator.

What Is a Power Converter?

A power converter is a tool that takes a power value in one unit and returns the equivalent value in any other supported unit. It works by routing every conversion through a single base unit, the watt, using each unit's defined factor: 1 kilowatt is exactly 1000 W, 1 megawatt is exactly 1,000,000 W, 1 mechanical horsepower is exactly 745.6998715822702 W (= 550 ft·lbf/s, via the IYP 1959 inch and the CGPM 1901 standard gravity), 1 metric horsepower (PS, CV, ch, л.с.) is exactly 735.49875 W (= 75 kgf·m/s, CGPM 1901), 1 electric horsepower is exactly 746 W (IEEE C57.12.00), 1 BTU (IT) per hour is 1055.05585262 J ÷ 3600 s ≈ 0.29307 W, 1 thermochemical kilocalorie per hour is 4184 J ÷ 3600 s ≈ 1.16222 W, and 1 foot-pound per second is exactly 1.3558179483314003 W. These are not engineering approximations: NIST SP 811 Appendix B.8 prints the SI and IYP factors in boldface (exact), and the watt itself is the SI coherent derived unit for power per BIPM SI Brochure 9th ed., Table 4.

This converter supports 9 units across four groups. The SI group covers the watt, kilowatt and megawatt — the natural choice for any modern engineering datasheet. The horsepower group is where most real-world confusion lives: mechanical horsepower (US/UK automotive, dyno specs), metric horsepower (the PS / CV / ch / л.с. printed on every EU car spec sheet — Porsche says "PS", Renault and Peugeot say "ch", Lada and KAMAZ say "л.с."), and electric horsepower (US motor nameplate convention, rounded to 746 W for cleaner electrical math). The thermal group covers BTU (IT) per hour, the unit on every US air-conditioner nameplate, and kilocalorie per hour, used in calorimetry, food-science process engineering and some European HVAC contexts. The gravitational group covers the foot-pound per second, the imperial work-rate unit underlying the mechanical horsepower definition and still used in some US industrial torque-and-speed calculations.

What distinguishes a serious power converter from a marketing widget is honesty about the three-horsepower problem and about IEEE-754 representation of per-hour factors. Three numerically distinct "horsepower" units coexist: mechanical hp (745.6998… W), metric hp / PS (735.49875 W), and electric hp (746 W). They differ by up to ~10 W per hp — a 1.4% spread between mechanical hp and PS, and a fixed +0.3 W between mechanical and electric hp. For a 510-horsepower spec the gap between reading it as PS vs mechanical hp is about 5 kW — enough to misstate a power-to-weight ratio when comparing a German GT against a US muscle car. This calculator surfaces all three explicitly, so an engineer importing a JDM or EU spec sheet sees which hp variant applies. The seven SI / hp / ft·lbf-per-second factors are tagged exact in the source data; BTU/h and kcal/h are tagged inexact because the 3600 in the per-hour denominator (the SI second is exact, but 1055.05585262/3600 cannot be represented as a finite binary fraction) carries a few ulps of representational drift in IEEE-754 doubles. The badge tells the truth about which is which.

How to Convert Between Power Units

Every power conversion is one multiplication and one division through the watt. The general formula is:

y = x \cdot \frac{a_{\text{from}}}{a_{\text{to}}}

where $x$ is your input value, $a_\text{from}$ is the source unit's factor to watts, and $a_\text{to}$ is the target unit's factor to watts. To do it by hand:

1. Look up the source-to-watt factor. For metric horsepower (PS), $a_\text{from} = 735.49875$ (exact, CGPM 1901).

2. Multiply the input by that factor to get watts. 510 PS × 735.49875 = 375,104.36 W.

3. Look up the target-to-watt factor. For kilowatts, $a_\text{to} = 1000$.

4. Divide the watt value by the target factor. 375,104.36 ÷ 1000 = 375.10 kW.

The same procedure works for every supported unit. Going from a "510 hp (mechanical)" US spec to kW instead: 510 × 745.6998715822702 ÷ 1000 = 380.31 kW. The 5-kW gap between 375.10 kW (PS) and 380.31 kW (mech) is real — the same nominal "510" hp number is two different power outputs depending on which standard the manufacturer used. Going from BTU/h to kW for HVAC sizing: 12,000 BTU/h × (1055.05585262 ÷ 3600) ÷ 1000 = 3.517 kW — the canonical 1-ton air conditioner, cross-checkable against the energy converter (12,000 BTU/h × 1 h = 12,000 BTU = 12.66 MJ of cooling delivered per hour). Going from a US electric-motor nameplate "50 hp" to kW: 50 × 746 ÷ 1000 = 37.3 kW exact (IEEE C57.12.00 round-number convention).

To use this calculator, pick the source unit from the "From" dropdown, type a value, then pick the target unit from the "To" dropdown. The result updates on every keystroke. Click the result card to copy it to the clipboard. Use the precision selector to switch between auto (6 significant figures), or a fixed 0, 2, 4, 6, 10 or 15 decimals. Auto-precision switches to scientific notation when the result exceeds 10¹² (one trillion) or falls below 10⁻³, so a megawatt-scale wind-farm rating converted to BTU/h still renders readably. The exact badge appears on rad-free SI-to-SI, SI-to-hp, hp-to-hp and ft·lbf/s pairs (7 of 9 units are tagged exact); the badge is withheld on any pair that touches BTU/h or kcal/h because the per-hour ratio (a NIST-exact joule value divided by 3600 s) cannot be represented as a finite binary fraction in IEEE-754. The cross-link note shown below the converter spells out the three-horsepower disambiguation so you never accidentally substitute one variant for another.

Power Conversion Formula

y = x \cdot \frac{a_{\text{from}}}{a_{\text{to}}}

$y$ = The converted value, expressed in the target unit of power.
$x$ = The input value, expressed in the source unit of power.
$a_{\text{from}}$ = Factor that converts the source unit to watts (e.g. 745.6998715822702 for mechanical hp, 735.49875 for metric hp / PS, 746 for electric hp).
$a_{\text{to}}$ = Factor that converts the target unit to watts (e.g. 1000 for kW, 1055.05585262/3600 for BTU/h, 1.3558179483314003 for ft·lbf/s).

The formula is a two-step pivot through the watt, the SI coherent derived unit for power (BIPM SI Brochure 9th ed., Table 4). The factor table this calculator uses is sourced from NIST SP 811 Appendix B.8, the CGPM 1901 standard-gravity resolution that anchors the metric horsepower, the International Yard and Pound Agreement of 1959 that anchors the mechanical horsepower, and IEEE C57.12.00 for the US electric horsepower:

Watt (W): 1 W (SI coherent derived unit, exact)
Kilowatt (kW): 10³ W (exact, SI prefix)
Megawatt (MW): 10⁶ W (exact, SI prefix)
Mechanical horsepower (hp): 745.6998715822702 W exact (= 550 ft·lbf/s, via IYP 1959 inch and CGPM 1901 standard gravity g_n = 9.80665 m/s²)
Metric horsepower / PS / CV / ch / л.с. (hp_metric): 735.49875 W exact (= 75 kgf·m/s, CGPM 1901)
Electric horsepower (hp_E): 746 W exact (IEEE C57.12.00 for US motor nameplates)
BTU (IT) per hour (BTU/h): 1055.05585262 ÷ 3600 ≈ 0.29307107017222 W (NIST-exact upstream values; representationally inexact in IEEE-754 because of the 3600 denominator)
Thermochemical kilocalorie per hour (kcal/h): 4184 ÷ 3600 ≈ 1.16222222222 W (legally exact ratio; representationally inexact)
Foot-pound per second (ft·lbf/s): 1.3558179483314003 W exact (= 1 lb·ft/s, identical to the torque ratio because the second pulls out as a scalar)

For the metric-hp → kW direction the calculator computes 1 PS × 735.49875 ÷ 1000 = 0.73549875 kW exact. For 1 mechanical hp → kW: 745.6998715822702 ÷ 1000 = 0.7456998715822702 kW exact. For 1 electric hp → kW: 746 ÷ 1000 = 0.746 kW exact. For 12,000 BTU/h → kW: 12,000 × (1055.05585262/3600) ÷ 1000 ≈ 3.51685 kW — tagged inexact because 1055.05585262/3600 ≈ 0.293071070172222… is non-terminating in binary. Every SI-to-SI and SI-to-hp conversion in this set earns the exact badge because every factor is a definitional rational (NIST-exact upstream); the thermal-rate pairs are honestly tagged inexact, matching how NIST itself prints the implied power factor as a non-boldface derived value in SP 811.

Worked Power Conversion Examples

510 PS to kilowatts (EU car-spec reconciliation, three-hp problem)

Set From = Metric horsepower (PS), To = Kilowatt, Value = 510. The formula gives 510 × 735.49875 ÷ 1000 = 375.10 kW exact. Now switch From = Mechanical horsepower and re-enter 510: the result is 510 × 745.6998715822702 ÷ 1000 = 380.31 kW. The same nominal number — 510 — is two different power outputs depending on which standard the manufacturer used. EU automotive datasheets (Porsche "510 PS", Mercedes-AMG, BMW M, Audi RS, Ferrari, Lamborghini) use the metric horsepower; US/UK datasheets (Ford GT, Corvette Z06, Dodge Hellcat, Aston Martin) use the mechanical horsepower. Misreading PS as mechanical hp inflates the kW figure by ~1.4%; misreading mech hp as PS deflates it by the same fraction. When you compare power-to-weight ratios across markets, this is the single biggest silent error to watch for.

12,000 BTU/h to kilowatts (HVAC sizing pipeline, 1-ton AC)

Set From = BTU per hour, To = Kilowatt, Value = 12000. The formula gives 12,000 × (1055.05585262/3600) ÷ 1000 ≈ 3.51685 kW of thermal capacity — the canonical "1-ton" air conditioner (the ton here is the cooling power needed to melt one short ton of ice per day, ≈ 12,000 BTU/h). A 24,000 BTU/h unit is a 2-ton AC ≈ 7.03 kW, suitable for about 1,100 ft² in temperate climates; a 36,000 BTU/h unit is a 3-ton AC ≈ 10.55 kW. The result is tagged inexact (no exact badge) because BTU/h carries the 3600-denominator IEEE-754 drift, even though the upstream BTU_IT = 1055.05585262 J value is exact by NIST. For the energy delivered, not the rate, cross-link to the energy converter: 12,000 BTU × 1 hour = 12.66 MJ of cooling per operating hour.

50 hp US electric motor to kilowatts (industrial nameplate)

Set From = Electric horsepower, To = Kilowatt, Value = 50. The formula gives 50 × 746 ÷ 1000 = 37.3 kW exact. US electric-motor nameplates use the IEEE C57.12.00 convention of 746 W per hp (about 0.04% above mechanical hp) precisely so the kW conversion gives round-number values useful in electrical sizing. A 100 hp_E motor is exactly 74.6 kW; a 200 hp_E motor is exactly 149.2 kW. If you read "50 hp" on a US motor and assume mechanical hp, you compute 37.28 kW — a 20 W difference, negligible for sizing but visible in efficiency calculations and rebate paperwork. The exact badge applies because both hp_E (746 W exact) and kW (10³ W exact) are definitional rationals.

1 MW wind turbine to mechanical horsepower (renewable-energy framing)

Set From = Megawatt, To = Mechanical horsepower, Value = 1. The formula gives 1,000,000 ÷ 745.6998715822702 ≈ 1,341.02 hp. A modern 3-MW onshore wind turbine is about 4,023 hp; a 100-MW wind farm aggregates to ≈ 134,102 hp_mech or ≈ 135,962 PS — but renewable-energy datasheets almost never quote horsepower because the historical hp unit is too small to make turbine ratings legible. Solar PV is in the same regime: a typical 5-10 kW residential array equals 6.7-13.6 PS, which is the rated power of a small motorcycle engine; nobody on a solar quote talks PS. The takeaway: SI units (kW, MW, GW) dominate the modern energy industry; the horsepower family lives almost exclusively in automotive, marine, aviation piston-engine, and industrial-motor namespaces.

1 hp_mech to ft·lbf/s (the definitional check)

Set From = Mechanical horsepower, To = Foot-pound per second, Value = 1. The formula gives 745.6998715822702 ÷ 1.3558179483314003 = 550 ft·lbf/s exact. This is the *definition* of the mechanical horsepower: 1 hp_mech = 550 ft·lbf/s, the unit James Watt selected in 1782 to compare his steam engines to actual dray horses lifting buckets out of a coal pit. The chain that anchors it is rigorous: the IYP 1959 fixes the international foot at 0.3048 m exactly; the avoirdupois pound is 0.45359237 kg exactly; the CGPM 1901 fixes standard gravity g_n at 9.80665 m/s² exactly. Multiplying through gives 745.6998715822702 W — every digit is meaningful, exact in symbolic form, exact to displayed precision in IEEE-754.

Comparative table: 1 unit in watts

Unit	Symbol	Value in watts	Exact?
BTU (IT) per hour	BTU/h	0.293071…	no (3600 denom)
Kilocalorie per hour	kcal/h	1.16222…	no (3600 denom)
Watt	W	1	yes
Foot-pound per second	ft·lbf/s	1.3558179483314003	yes
Metric horsepower / PS	hp_metric	735.49875	yes
Mechanical horsepower	hp	745.6998715822702	yes
Electric horsepower	hp_E	746	yes
Kilowatt	kW	1,000	yes
Megawatt	MW	1,000,000	yes

Use this table to do conversions by hand: divide source-in-watts by target-in-watts. For example, 1 mechanical hp in PS = 745.6998715822702 ÷ 735.49875 = 1.01387 PS — the canonical 1.4% spread. 1 kW in mechanical hp = 1000 ÷ 745.6998715822702 = 1.34102 hp. 1 kW in PS = 1000 ÷ 735.49875 = 1.35962 PS (the conversion you need when reading EU car specs in a US engineering context).

Most common power conversions

These are the unit pairs people look up most often. Use them as a quick reference, or paste them into the calculator for an exact result to 15 decimals.

Kilowatt to mechanical horsepower: 1 kW ≈ 1.34102 hp (exact = 1000/745.6998715822702)
Kilowatt to metric horsepower (PS): 1 kW ≈ 1.35962 PS (exact = 1000/735.49875)
Kilowatt to electric horsepower: 1 kW ≈ 1.34048 hp_E (exact = 1000/746)
Mechanical hp to kW: 1 hp = 0.7456998715822702 kW (exact)
Metric hp (PS) to kW: 1 PS = 0.73549875 kW (exact)
Electric hp to kW: 1 hp_E = 0.746 kW (exact)
Mechanical hp to PS: 1 hp ≈ 1.01387 PS (the 1.4% three-hp gap)
Metric hp (PS) to mechanical hp: 1 PS ≈ 0.98632 hp
BTU/h to watt: 1 BTU/h ≈ 0.29307 W (1055.05585262/3600, IEEE-754 inexact)
BTU/h to kW: 3,412.14 BTU/h ≈ 1 kW (engineering rule of thumb)
12,000 BTU/h to kW: 12,000 BTU/h ≈ 3.51685 kW (1-ton AC)
Kilocalorie/h to watt: 1 kcal/h ≈ 1.16222 W
Foot-pound/s to watt: 1 ft·lbf/s = 1.3558179483314003 W (exact)
550 ft·lbf/s to hp: 550 ft·lbf/s = 1 hp_mech exact (the definition)

Power Conversion Tips

Pivot through the watt. Every conversion in this tool is implemented as "input × from-factor ÷ to-factor", with the watt as the pivot. Memorising five factors gives you every cross-conversion: kilowatt (1000), mechanical hp (745.6998715822702), metric hp / PS (735.49875), electric hp (746), and BTU/h (1055.05585262/3600 ≈ 0.29307).
Treat "horsepower" as ambiguous until you know the source. If you see "hp" on a US/UK car spec, assume mechanical hp (550 ft·lbf/s, 745.7 W). If you see "PS", "CV", "ch" or "л.с." on a German, French, Italian, Spanish, or Russian spec, it is metric horsepower (75 kgf·m/s, 735.5 W). If you see "hp" on a US electric-motor nameplate, it is electric hp (746 W exact per IEEE C57.12.00). The three differ by up to ~10 W per hp — a 1.4% spread between mech and PS, and +0.3 W between mech and electric — which adds up to several kW at supercar power levels.
Remember the 510-PS Porsche example as the canonical sanity check. A Porsche 911 GT3 rated at 510 PS is 375.10 kW; reading the same spec sheet as 510 hp_mech inflates the number to 380.31 kW. A 5-kW discrepancy is real and visible in power-to-weight comparisons: a 1,435 kg car at 375 kW is 261 W/kg; at 380 kW it is 265 W/kg, a meaningful difference when comparing GT3 against US muscle on the same scale.
For HVAC sizing, remember 12,000 BTU/h ≈ 3.517 kW = 1 ton of cooling. The "ton" is a legacy from ice-house economics: the cooling power needed to melt one short ton of ice per day. A 24,000 BTU/h unit is a 2-ton AC ≈ 7 kW; a 36,000 BTU/h unit is a 3-ton AC ≈ 10.5 kW. Sizing rule of thumb in temperate climates: 20 BTU/h per ft² of conditioned floor space — so a 1,500 ft² home wants about 30,000 BTU/h ≈ 8.8 kW = 2.5 tons.
Read the "exact" badge as a statement about IEEE-754 representation, not mathematical definition. All nine units in this calculator are defined exactly by their respective standards (NIST SP 811, CGPM 1901, IYP 1959, IEEE C57.12.00). The badge withholds itself on BTU/h and kcal/h because their watt-equivalent factors carry a 3600 denominator that cannot be represented as a finite binary fraction in 64-bit floating point — a few ulps of drift, not a definitional fuzziness. Compare with the angle converter, where every π-derived factor is tagged approximate because π is irrational.
For industrial motor specs, multiply electric hp by 0.746 to get kW exactly. A 5 hp_E motor is 3.73 kW exact; a 10 hp_E is 7.46 kW; a 25 hp_E is 18.65 kW; a 50 hp_E is 37.3 kW; a 100 hp_E is 74.6 kW; a 200 hp_E is 149.2 kW. The round-number convention is by design (IEEE C57.12.00) — it makes branch-circuit and overload sizing cleaner. Note this is *electrical* hp; the *output* shaft power may be smaller because of motor efficiency (typically 85-95% for industrial induction motors).
Use the foot-pound per second to sanity-check torque × speed calculations. Power (W) = torque (N·m) × angular velocity (rad/s). The imperial equivalent is power (ft·lbf/s) = torque (lbf·ft) × angular velocity (rad/s) — and 550 ft·lbf/s is exactly 1 mechanical hp. So a 200 lbf·ft engine spinning at 5,500 rpm (≈ 576 rad/s) delivers 200 × 576 ÷ 550 ≈ 209 hp; cross-check by converting torque to N·m (271 N·m) and speed to rad/s, then multiplying for kW, then converting kW back to hp — both paths must agree to the displayed precision.
For renewable energy and grid-scale work, stay in SI. A residential solar array is 5-10 kW; a commercial array is 100 kW – 1 MW; a utility-scale solar farm is 10-500 MW; a typical onshore wind turbine is 2-5 MW; a nuclear reactor unit is ~1 GW (= 1,000 MW). Quoting any of these in horsepower is meaningless because the historical hp unit (≈ 0.75 kW) is far too small — a 1 GW reactor would need 1,341,022 hp_mech, an unhelpful number for any audience.
When the result is bigger than 10¹² (one trillion) or smaller than 10⁻³ at auto-precision, the display switches to scientific notation. This is on purpose: converting a single watt to BTU per hour gives 3.412 BTU/h (readable), but converting a microwatt to mechanical hp gives 1.341 × 10⁻⁹ hp — readable in scientific notation, unreadable as 0.000000001341 hp.

Power Converter — Frequently Asked Questions

Is this power converter free?

Yes. The calculator is free, requires no account, runs entirely in your browser, and is ad-free. The embeddable iframe version at /widget/power-converter is also free and ad-free, so you can drop it into automotive forums, HVAC design tools, motor-specifier portals, or engineering teaching materials without exposing readers to third-party trackers.

What is the difference between mechanical, metric, and electric horsepower?

Mechanical hp is 745.6998715822702 W exact (= 550 ft·lbf/s, used in US and UK automotive specs). Metric hp / PS is 735.49875 W exact (= 75 kgf·m/s, used in EU, Japanese, Russian and most non-Anglo car specs — labelled PS in Germany, CV in Spain/France/Italy, ch in France, л.с. in Russian). Electric hp is 746 W exact (IEEE C57.12.00, US motor nameplate convention). The mech-to-PS gap is about 1.4%; the mech-to-electric gap is +0.04%.

How accurate are the conversion factors?

Seven of the nine unit factors are exact in IEEE-754: watt, kilowatt, megawatt, mechanical hp (745.6998715822702 W via IYP 1959 + CGPM 1901), metric hp (735.49875 W via CGPM 1901), electric hp (746 W exact per IEEE C57.12.00), and foot-pound per second (1.3558179483314003 W). The BTU/h and kcal/h factors are mathematically exact by definition (1055.05585262 J ÷ 3600 s and 4184 J ÷ 3600 s) but representationally inexact because the 3600 second denominator cannot be exactly represented as a binary fraction in 64-bit floating point. The calculator labels those two units inexact to be honest with you.

How do I convert PS to kW?

Multiply by 0.73549875. So 510 PS × 0.73549875 = 375.10 kW. The factor is exact by CGPM 1901 (1 PS = 75 kgf·m/s with g_n = 9.80665 m/s²). If you instead read the spec as mechanical hp, multiply by 0.7456998715822702 — a 510-hp_mech reading gives 380.31 kW, a 5-kW overstatement of the same nominal number.

How do I convert kilowatts to horsepower?

Divide by 0.745699871582 for mechanical hp (1 kW ≈ 1.34102 hp), by 0.73549875 for metric hp / PS (1 kW ≈ 1.35962 PS), or by 0.746 for US electric hp (1 kW ≈ 1.34048 hp_E).

What is 12,000 BTU/h in kilowatts?

About 3.517 kW. The exact computation is 12,000 × (1055.05585262 ÷ 3600) ÷ 1000 = 3.51685 kW. This is the canonical "1 ton" air conditioner rating — the cooling power needed to melt one short ton of ice per day. A 24,000 BTU/h unit is a 2-ton AC ≈ 7.03 kW; a 36,000 BTU/h is a 3-ton AC ≈ 10.55 kW.

Why is electric horsepower exactly 746 watts?

Because IEEE C57.12.00 (the US standard for distribution transformers and adjacent motor work) defines it that way for clean electrical math. 746 W is about 0.04% above the mechanical horsepower (745.6998… W) — a deliberately rounded value so a US 100 hp electric motor is exactly 74.6 kW on its nameplate. The mechanical horsepower keeps its IYP-anchored irrational-looking decimal because it is anchored to the foot, the pound, and standard gravity, none of which round to 746 W when combined.

What does PS stand for and where is it used?

PS stands for PferdeStärke, German for "horse-strength". It is the same unit as the French CV / ch (cheval-vapeur), the Italian and Spanish CV (caballo de vapor), the Russian л.с. (лошадиная сила), the Japanese 馬力, and the international "metric horsepower": 735.49875 W exact, defined by CGPM 1901 as 75 kgf·m/s with standard gravity g_n = 9.80665 m/s² exact. Every EU automotive spec sheet uses PS (or its local-language equivalent); US and UK spec sheets use mechanical hp.

How many BTU per hour is one kilowatt?

About 3,412.14 BTU/h per kW. The exact computation is 3600 ÷ 1.05505585262 = 3,412.14163… BTU/h per kW. This is the engineering rule of thumb HVAC contractors memorise: 1 kW ≈ 3.4 kBTU/h. Going the other way, 1 BTU/h ≈ 0.293 W.

Is 1 horsepower really the power of one horse?

Approximately, for short bursts. James Watt set the figure in 1782 by watching dray horses lift coal from a pit; he measured roughly 33,000 ft·lbf per minute = 550 ft·lbf/s sustained, and used that as a benchmark to sell steam engines ("this engine replaces N horses"). A healthy draft horse can produce 1 hp continuously and burst to 10-15 hp for a few seconds. A trained human cyclist sustains about 0.3 hp (≈ 225 W) for an hour and bursts to about 2 hp.

What is the difference between a kilocalorie per hour and a kilowatt?

1 kcal/h ≈ 1.16222 W. So 1 kW ≈ 860.42 kcal/h, and 1,000 kcal/h ≈ 1.162 kW. Kilocalorie per hour shows up in food-science process engineering, calorimetry, and some European HVAC documents; SI engineering and modern HVAC mostly use kW directly. The cal_th = 4.184 J convention is used in this calculator (NIST SP 811 boldface).

Can I embed this converter on my site?

Yes. The embeddable version lives at /widget/power-converter; copy the iframe snippet from the embed page. The iframe is ad-free, dependency-free, mobile-responsive, and inherits no third-party trackers — useful for automotive blogs, HVAC design portals, motor-specifier intranets, and engineering teaching materials that want a clean power converter without sending readers off-site.

Why does 1 mechanical horsepower come out to 745.6998715822702 watts and not a round number?

Because it is defined as 550 ft·lbf/s, and the chain that converts ft, lb and g_n to SI units involves three exact but non-decimal-friendly rationals: 1 ft = 0.3048 m exactly (IYP 1959), 1 lb = 0.45359237 kg exactly (IYP 1959), g_n = 9.80665 m/s² exactly (CGPM 1901). Multiplying 550 × 0.3048 × 0.45359237 × 9.80665 yields 745.6998715822702 W — every digit is meaningful and exact, just not round.

Key Power Conversion Terms

Watt (W)

The SI coherent derived unit for power (BIPM SI Brochure 9th ed., Table 4). One watt equals one joule per second, or one volt times one ampere. The watt is the base unit through which this calculator routes every conversion.

Kilowatt (kW)

Exactly 1,000 watts (SI prefix). Standard for residential electrical loads, EV charging, small motors, and modern engineering datasheets. A typical home draws 1-3 kW average; a Level 2 EV charger delivers 7-19 kW; a small electric motor is 1-10 kW.

Megawatt (MW)

Exactly 1,000,000 watts (SI prefix). Standard for grid-scale generation: a typical onshore wind turbine is 2-5 MW; a utility solar farm is 10-500 MW; a nuclear reactor unit is ~1 GW = 1,000 MW. The horsepower family is rarely used at this scale because hp is too small to render the numbers legibly.

Mechanical horsepower (hp)

Exactly 745.6998715822702 W (= 550 ft·lbf/s, via IYP 1959 inch and CGPM 1901 standard gravity). The horsepower used in US and UK automotive spec sheets, dyno reports, and most English-language engineering. Named for James Watt's 1782 estimate of one horse's sustained output. Also called imperial horsepower (Wikidata Q2276380).

Metric horsepower / PS / CV / ch / л.с. (hp_metric)

Exactly 735.49875 W (= 75 kgf·m/s with g_n = 9.80665 m/s², CGPM 1901). The horsepower printed on every EU automotive spec — "PS" (PferdeStärke) in Germany, "CV" in Spain and Italy, "ch" in France, "л.с." in Russian, "馬力" in Japanese. About 1.4% smaller than mechanical horsepower (Wikidata Q160857).

Electric horsepower (hp_E)

Exactly 746 W (IEEE C57.12.00). Used on US electric-motor nameplates to give round-number kW values (1 hp_E = 0.746 kW exactly). About 0.04% above mechanical horsepower; the rounding is deliberate for cleaner branch-circuit sizing math (Wikidata Q104907442).

BTU per hour (BTU/h)

The IT British thermal unit per hour, exactly 1055.05585262 J ÷ 3600 s ≈ 0.29307 W. Standard on US air-conditioner nameplates; 12,000 BTU/h = 1 ton of cooling ≈ 3.517 kW. The watt-equivalent factor is representationally inexact in IEEE-754 because the 3600 second denominator is not a finite binary fraction, even though both upstream values (BTU_IT in joules, SI second) are exact.

Kilocalorie per hour (kcal/h)

Thermochemical kilocalorie per hour, exactly 4184 J ÷ 3600 s ≈ 1.16222 W. Used in food-science process engineering, calorimetry, and some European HVAC contexts. Same IEEE-754 caveat as BTU/h: the legal definition is exact (NIST SP 811 boldface 4.184 J/cal_th), but the per-hour ratio carries representational drift.

Foot-pound per second (ft·lbf/s)

The imperial work-rate unit, exactly 1.3558179483314003 W (= 1 lb·ft/s — same number as the torque-to-N·m ratio because the second pulls out as a scalar). 550 ft·lbf/s defines the mechanical horsepower exactly. Still used in US industrial torque-and-speed calculations and in classical mechanics teaching.

Standard gravity (g_n)

The conventional reference value of Earth's gravitational acceleration, fixed by the 3rd CGPM in 1901 at exactly 9.80665 m/s². It anchors the metric horsepower (75 kgf·m/s) and, via the kilogram-force, the entire kgf/lbf family. Not the actual local gravity (which varies ±0.5% across Earth's surface) — a defined constant.

IYP 1959 (International Yard and Pound Agreement)

The 1959 international treaty that fixed the inch at exactly 25.4 mm, the foot at exactly 0.3048 m, and the avoirdupois pound at exactly 0.45359237 kg. Combined with CGPM 1901 standard gravity, this gives the exact conversion 1 mechanical hp = 745.6998715822702 W.

IEEE C57.12.00

The IEEE standard for general requirements for liquid-immersed distribution, power, and regulating transformers. Codifies the US electric-horsepower convention of 1 hp_E = 746 W exact, used on US electric-motor nameplates for clean branch-circuit and overload sizing.

IEEE-754 double

The 64-bit floating-point format used by JavaScript and most calculators. It carries about 15-17 significant decimal digits. Most power-unit factors in this calculator (watt, kW, MW, mechanical hp, PS, electric hp, ft·lbf/s) are definitional rationals representable exactly to displayed precision. BTU/h and kcal/h are tagged inexact because their watt-equivalent factors have 3600 in the denominator, which is not a finite binary fraction — a few ulps of representational drift, honestly reported by withholding the exact badge.

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