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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.

hp

Result

0.7457 kW

1 hp= 0.7457 kW

UnitValue
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.

Energy ConverterTemperature Converter

Power converter. SI watts, three horsepower variants, and thermal units like BTU/h.

A power converter routes any value through the watt to give you the equivalent in 8 other units, keeping the three different horsepower types apart. Useful for reading kW vs PS on a car spec, sizing an air conditioner from BTU/h, or decoding US datasheets in hp.

What Is a Power Converter?

Here is the catch that trips up everyone who quotes horsepower: "horsepower" is not one number. The mechanical horsepower used on US and UK car specs is about 745.7 W, but the metric horsepower stamped on every European spec sheet as PS, CV or ch is about 735.5 W, and there is a third electric horsepower defined at exactly 746 W for US motor nameplates. So the same "200 hp" engine can be quoted as three slightly different wattages depending on which standard the manufacturer used — a gap of up to ~10 W per horsepower that grows to several kilowatts at supercar power levels. A power converter has to be careful about exactly this.
It helps to remember that power is a rate, not an amount. A watt measures how fast energy flows (one joule every second); a watt-hour measures how much energy has flowed. That distinction is why a 3.5 kW air conditioner and a 3.5 kWh battery describe completely different things, and why a converter built for power must never be confused with one built for energy.
This calculator handles 9 power units across four families, and it routes every conversion through a single base unit — the watt — using each unit's defined factor. One kilowatt is exactly 1000 W and one megawatt is exactly 1,000,000 W. The three horsepower variants are mechanical hp at 745.6998715822702 W (= 550 ft·lbf/s, fixed by the 1959 International Yard and Pound Agreement plus standard gravity), metric hp / PS at 735.49875 W (= 75 kgf·m/s, CGPM 1901), and electric hp at exactly 746 W (IEEE C57.12.00). The thermal family covers BTU (IT) per hour at 1055.05585262 J ÷ 3600 s ≈ 0.29307 W and the thermochemical kilocalorie per hour at 4184 J ÷ 3600 s ≈ 1.16222 W. The gravitational family covers the foot-pound per second at exactly 1.3558179483314003 W. These are not engineering approximations: NIST SP 811 Appendix B.8 prints the SI and yard-pound factors in boldface (exact), and the watt is the SI coherent derived unit for power per the BIPM SI Brochure.
Seven of the nine factors (the three SI units, all three horsepower variants, and the foot-pound per second) are definitional rationals that store exactly in IEEE-754 double precision, so they carry an "exact" badge. BTU/h and kcal/h do not, because the per-hour denominator of 3600 cannot be written as a finite binary fraction — a few units in the last place of representational drift, honestly flagged rather than hidden. That honesty about which factor is exact is what separates a serious converter from a marketing widget, and it is exactly where most generic tools stay silent.

How to Convert Between Power Units

Every power conversion is one multiplication and one division through the watt. The general formula is:
y=x⋅afromatoy = x \cdot \frac{a_{\text{from}}}{a_{\text{to}}}
where x is your input value, a_from is the source unit's factor to watts, and a_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_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_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 (mechanical) is real — the same nominal "510" is two different power outputs depending on the standard. 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. 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, and you can tap the result card to copy it. Use the precision selector to switch between auto (6 significant figures) and a fixed 0, 2, 4, 6, 10 or 15 decimals; auto-precision drops into scientific notation above one trillion or below one thousandth so a megawatt-scale rating converted to BTU/h still renders readably. The "exact" badge appears on SI-to-SI, SI-to-hp, hp-to-hp and ft·lbf/s pairs (7 of 9 units), and is withheld on any pair touching BTU/h or kcal/h because the per-hour ratio carries IEEE-754 drift.

Most-Searched Power Conversions

FromToValueExact?
1 kilowattMechanical hp1.34102 hpyes
1 kilowattMetric hp (PS)1.35962 PSyes
1 kilowattElectric hp (hpE)1.34048 hpEyes
1 mechanical hpKilowatt0.745700 kWyes
1 metric hp (PS)Kilowatt0.73549875 kWyes
1 electric hp (hpE)Kilowatt0.746 kWyes
1 mechanical hpMetric hp (PS)1.01387 PSyes
1 kilowattBTU per hour3,412.14 BTU/hno (3600 denom)
12,000 BTU/h (1-ton AC)Kilowatt3.51685 kWno (3600 denom)
1 kilowattKilocalorie/h860.42 kcal/hno (3600 denom)
550 ft·lbf/sMechanical hp1 hp (the definition)yes

Power Conversion Formula

y=x⋅afromatoy = x \cdot \frac{a_{\text{from}}}{a_{\text{to}}}
  • yy = The converted value, expressed in the target unit of power.
  • xx = The input value, expressed in the source unit of power.
  • afroma_{\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).
  • atoa_{\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; 1 W = 1 J/s = 1 V·A). 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 and CGPM 1901 standard gravity gn = 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 (hpE): 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; 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 mechanical 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, 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. Remember the cooling rating is not the electrical draw: an efficient inverter unit delivers that 3.5 kW of cooling on roughly 1 kW of electricity.

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 hpE motor is exactly 74.6 kW; a 200 hpE motor is exactly 149.2 kW. If you read "50 hp" on a US motor and assume mechanical hp, you compute 37.28 kW — about a 15 W difference, negligible for sizing but visible in efficiency calculations and rebate paperwork. The exact badge applies because both hpE (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, 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, while the horsepower family lives almost exclusively in automotive, marine, aviation piston-engine, and industrial-motor contexts.

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 gn at 9.80665 m/s² exactly. Multiplying through gives 745.6998715822702 W — every digit is meaningful, exact in symbolic form and exact to displayed precision in IEEE-754.

Comparative table: 1 unit in watts

UnitSymbolValue in wattsExact?
BTU (IT) per hourBTU/h0.293071…no (3600 denom)
Kilocalorie per hourkcal/h1.16222…no (3600 denom)
WattW1yes
Foot-pound per secondft·lbf/s1.3558179483314003yes
Metric horsepower / PShp_metric735.49875yes
Mechanical horsepowerhp745.6998715822702yes
Electric horsepowerhpE746yes
KilowattkW1,000yes
MegawattMW1,000,000yes
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).

Power Converter — Frequently Asked Questions

Is this power converter free?

Yes. The calculator requires no account, runs entirely in your browser, and is ad-free. The embeddable iframe version at /widget/power-converter is also 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 mechanical-to-PS gap is about 1.4%; the mechanical-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 denominator cannot be stored as a finite 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 gn = 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 hpE).

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 covering 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 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, 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 gn = 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. 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. This calculator uses the thermochemical convention cal_th = 4.184 J (NIST SP 811 boldface).

Is power the same thing as energy?

No, and the converter only handles power. Power is a rate — the watt is one joule per second, telling you how fast energy flows. Energy is an amount — a watt-hour is the energy delivered by one watt running for one hour. A 3.5 kW air conditioner draws power; the 3.5 kWh it uses over an hour is energy. To convert joules, calories or watt-hours, use an energy converter instead.

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 gn 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), gn = 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.

Sources & References

  1. NIST SP 811 Appendix B.8 — Factors for units listed alphabetically (exact power factors: 1 mechanical hp = 745.6998715822702 W via IYP+g_n, 1 metric hp = 735.49875 W, 1 BTU_IT/h = 1055.05585262 J / 3600 s, 1 ft·lbf/s = 1.3558179483314003 W)
  2. NIST Guide to the SI, Appendix B — Conversion factors landing page (covers default 6-significant-figure engineering convention and the boldface = exact distinction used in the power and energy tables)
  3. BIPM SI Brochure (9th edition, Table 4) — defines the watt as the SI coherent derived unit for power (1 W = 1 J/s = 1 V·A)
  4. 3rd CGPM (1901), Resolution 2 — fixes standard gravity g_n at exactly 9.80665 m/s², which anchors both the metric horsepower (75 kgf·m/s) and the kilogram-force / pound-force chain used by the mechanical horsepower (550 ft·lbf/s)
  5. International Yard and Pound Agreement (1 July 1959) — fixes the international foot at exactly 0.3048 m and the avoirdupois pound at exactly 0.45359237 kg, the last two constants needed to make 1 mechanical hp = 745.6998715822702 W exact
  6. IEEE C57.12.00 — 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)
  7. Wikipedia — Horsepower (covers all three NIST-recognised variants: mechanical hp 745.6998… W, metric hp / PS 735.49875 W, electric hp 746 W; plus boiler, brake, water and indicated hp variants used in narrower industries)
  8. Wikipedia — Watt (SI coherent derived unit for power, 1 W = 1 J/s, named after James Watt who chose the horsepower benchmark in 1782)
  9. German Wikipedia — Pferdestärke (canonical reference for the PS / CV / ch / л.с. metric horsepower used in EU, Japanese, and Russian automotive specifications; 1 PS = 75 kp·m/s = 735.49875 W exact)

Content verified by the Smart Calculators Team