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.

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업데이트됨: 2026년 7월 18일

Power converter: watts, kilowatts, horsepower and BTU/h.

Enter a value in watts, kilowatts, horsepower or BTU/h and this converter returns the matching figure in every other power unit, computed through the watt. Its main job is telling the three horsepowers apart — mechanical hp at 745.7 W, metric hp (PS) at 735.5 W, and electric hp at 746 W.

What Is a Power Converter?

Here is the catch that trips up everyone who quotes horsepower: "horsepower" is not a single number. The figure on a US or UK car spec is the mechanical horsepower, worth about 745.7 W — the unit James Watt pinned to 550 foot-pounds per second back in the 1780s. The PS printed on European spec sheets is a different unit, the metric horsepower, worth 735.5 W. And a third value, the electric horsepower at exactly 746 W, is what US motor nameplates use for clean electrical math. Mechanical and metric hp sit about 1.4% apart, so the same "400 hp" can describe three slightly different engines depending on who wrote the number down.

Power is also easy to mistake for energy, and the two are not interchangeable. A watt is a rate — how fast energy moves — while a watt-hour is an amount, the energy delivered by one watt over an hour. That is why a 3.5 kW air conditioner and a 3.5 kWh battery describe completely different things, and why converting power on this page is a separate job from converting energy such as joules, kWh or calories.

To keep all of that straight, the converter sends every value through one base unit — the watt — and reads it back out in whatever unit you asked for, so watts to horsepower, kW to hp, or BTU/h to kW are all the same short calculation. The units group into the SI scale (watt, kilowatt, megawatt), the horsepower trio (mechanical, metric/PS, electric), the thermal pair used in heating and cooling (BTU per hour and kilocalorie per hour), and the older gravitational foot-pound per second. The everyday anchors people search for fall out at once: 1 kW is 1.34102 mechanical horsepower, and 1 W is 3.41214 BTU/h — the rule of thumb an HVAC installer leans on when a heat pump is rated in kilowatts.

How to Use the Power Converter

Pick the unit you are starting from in the From menu, pick the unit you want in the To menu, and type your number — the answer appears immediately and refreshes as you type. Tap the result to copy it. Because both menus hold the complete unit list, nothing forces you into a fixed pairing: watts to horsepower, kW to hp, hp to kW, or BTU/h to kW all behave the same way. When a result runs to many digits, the precision control lets you fix the number of decimals instead of the automatic display.

Working it by hand is two moves, because every unit is defined against the watt. First multiply your value by its watt factor to reach watts, then divide by the target unit's watt factor. Reading 510 PS from a European brochure into kilowatts: 510 × 735.5 is about 375,100 W, which is 375.1 kW. Take that same "510" as mechanical horsepower instead — 510 × 745.7 — and you land on 380.3 kW, a 5 kW gap from nothing but a mislabeled unit. Going the other direction for an HVAC nameplate, 1 W is 3.41214 BTU/h, so a 3.5 kW heat pump outputs roughly 11,900 BTU/h (3500 × 3.41214).

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The Power Conversion Formula

P_t = P_s × f_s ÷ f_t

$P_s$ = The power you start from, in the source unit
$f_s$ = Watts in one source unit — its factor to the watt (745.6998716 for mechanical hp, 735.49875 for metric hp/PS, 746 for electric hp)
$f_t$ = Watts in one target unit — its factor to the watt
$P_t$ = The converted power, in the target unit

Every power conversion is a single multiplication, because all power units share the same zero: zero of anything is zero watts. Give each unit one number — how many watts it equals — and any pair of units is two scalings apart. Scale the input up to watts with the source factor, then scale back down with the target factor. There is no offset to add, which is why watts to horsepower converts the same clean way as kW to BTU/h.

The catch specific to power is that the horsepower factor is not one number but three. Mechanical horsepower is 550 foot-pounds-force per second = 745.6998716 W, the value on US and UK car specs. Metric horsepower — the PS, CV or ch on European sheets — is 75 kilogram-force-metres per second = 735.49875 W exactly. Electric horsepower, on US motor nameplates, is a round 746 W. The SI units step by powers of ten: 1 kilowatt = 1000 W and 1 megawatt = 1,000,000 W. The older gravitational foot-pound per second is 1.3558179 W.

Most of these factors are exact definitions. The two thermal units are the exceptions: 1 BTU per hour is 1055.05585262 joules ÷ 3600 seconds = 0.293071 W, and 1 kilocalorie per hour is 4184 ÷ 3600 = 1.162222 W. That division by 3600 never terminates, so those two watt values are the rounded faces of a fraction — the only non-exact factors in the set. Everything else, including the everyday 1 kW = 1.34102 mechanical hp, is exact by definition; the 1.34102 is simply 1000 ÷ 745.6998716 rounded for display, and raising the precision brings the hidden digits back.

Common Power Conversions

Conversion	Result	Exact?
1 mechanical horsepower (US/UK cars)	745.7 watts	rounded
1 metric horsepower / PS (EU cars)	735.49875 watts	exact
1 electric horsepower (US motors)	746 watts	exact
1 kilowatt	1000 watts	exact
1 kilowatt	1.34102 mechanical hp	rounded
1 kilowatt	1.35962 metric hp (PS)	rounded
1 megawatt	1000 kilowatts	exact
1 watt	3.41214 BTU/h	rounded
1 kilowatt	3412.14 BTU/h	rounded
1 BTU/h	0.293071 watts	rounded
1 kilocalorie/h	1.16222 watts	rounded
1 foot-pound/second	1.35582 watts	rounded

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Worked Power Conversions

US dyno: 224 kW in mechanical horsepower

A tuning-shop dyno that logs 224 kW at the wheels reads 300 mechanical horsepower. Multiply kilowatts by 1.34102, the mechanical-hp factor US and UK shops use: 224 × 1.34102 = 300.4 hp, rounded to 300. Reverse it by multiplying horsepower by 0.7457 (745.7 W each), so 300 hp returns to about 223.7 kW. Read that same 224 kW off a European sheet and it prints as 224 × 1.35962 = 304.6 PS — a bigger number for the identical engine, because the PS is the smaller unit.

European car: 510 PS in kilowatts

A European brochure quoting 510 PS is 375.1 kW. Multiply PS by 0.73549875, since one metric horsepower is 735.49875 W: 510 × 0.73549875 = 375.1 kW. The trap is the horsepower line — 510 PS is only 503 mechanical hp (510 × 0.98632), not 510 hp, because the PS is about 1.4% smaller. Report it as "510 hp" on a US spec sheet and you overstate the engine by roughly 7 hp, enough to skew a power-to-weight comparison across markets.

Motor nameplate: 10 hp in watts

How many watts a 10 hp motor represents depends on which horsepower the nameplate means. As mechanical hp it is 7457 W (10 × 745.7), or 7.457 kW. A US electric-motor nameplate uses electric hp instead — 10 × 746 = 7460 W — just 3 W more, so at motor sizes the two are effectively identical. Read the same plate as 10 PS, though, and you would get 10 × 735.5 = 7355 W, about 100 W low. To go back, divide watts by the matching factor: 7457 ÷ 745.7 = 10 hp.

HVAC: a 3.5 kW heat pump in BTU/h

A heat pump rated 3.5 kW of heat output moves about 11,940 BTU/h. Multiply watts by 3.41214: 3500 × 3.41214 = 11,942 BTU/h, essentially the 12,000 BTU/h of a "1-ton" unit. Reverse it — 12,000 BTU/h × 0.293071 = 3517 W = 3.52 kW. One caution: this BTU/h is the heat the unit moves, not the electricity it draws. An efficient compressor might pull only about 1 kW from the wall to shift 3.5 kW of heat, which is why the BTU/h nameplate and the electricity bill never match.

Utility scale: 3 MW in horsepower

A 3 MW wind turbine is about 4023 mechanical horsepower. A megawatt is a million watts, so 3 MW is 3000 kW; multiply by 1.34102 to get 3000 × 1.34102 = 4023 mechanical hp, or divide 3,000,000 W by 745.7 for the same result. That is the scale where the watt family takes over from horsepower — power plants, ship engines and grid equipment are quoted in megawatts, and the horsepower figure is mostly there to make the number relatable.

Common Power Conversion Mistakes

Assuming every "horsepower" is the same unit. Three are in daily use: mechanical (imperial) hp at 745.7 W on US and UK car specs, metric hp — labeled PS, CV or ch — at 735.5 W on European, Japanese and most other specs, and electric hp at exactly 746 W on US motor nameplates. Mechanical and metric hp sit about 1.4% apart, so treating a European PS figure as mechanical hp quietly inflates the wattage.
Confusing power with energy. A kilowatt (kW) is a rate; a kilowatt-hour (kWh) is an amount — the energy used when 1 kW runs for one hour. This converter cannot turn kW into kWh, because that needs a time span. If your figure carries an "-hour" (Wh, kWh), it is energy and belongs in an energy converter, not here.
Reading a PS or CV number as mechanical hp. European brochures quote metric horsepower (735.5 W); US and UK brochures quote mechanical horsepower (745.7 W). Take a "510 PS" car as 510 mechanical hp and you overstate it by about 5 kW — enough to skew any power-to-weight comparison across markets. Match the horsepower type to where the spec was written before you convert.
Mixing up BTU/h with BTU. BTU per hour is power — a rate of heat flow, and what furnace and air-conditioner nameplates quote. A plain BTU with no "per hour" is energy, a fixed amount of heat. This converter handles BTU/h; a bare BTU figure belongs with energy units. Since 1 W is 3.41214 BTU/h, a 1 kW heater outputs about 3412 BTU/h.
Reading an AC's BTU/h rating as its electricity use. The BTU/h on an air-conditioner label is cooling power — the heat it can move — not the power it pulls from the socket. A 12,000 BTU/h (3.52 kW) unit may draw only about 1 kW of electricity, because a heat pump moves more heat than the energy it consumes. Use the BTU/h figure to size the room and the wattage or SEER rating to estimate the running cost.

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Power Converter — Frequently Asked Questions

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

Mechanical (imperial) horsepower is 745.7 W and appears on US and UK car specs. Metric horsepower — written PS in Germany, CV in France, Spain and Italy, or ch in France — is 735.5 W and is used across Europe, Japan and most other markets. Electric horsepower is exactly 746 W, the round value on US motor nameplates. Mechanical and metric hp differ by about 1.4%.

How many watts are in one horsepower?

It depends on which horsepower. Mechanical (US/UK car) horsepower is 745.7 W, metric horsepower (PS/CV) is 735.5 W, and electric horsepower on US motor nameplates is exactly 746 W. When people say "1 hp is 746 watts," they mean the electric one.

How do I convert kilowatts to horsepower?

Multiply kilowatts by 1.34102 to get mechanical horsepower, so 150 kW is about 201 hp. For metric horsepower (PS) — the European unit — multiply by 1.35962 instead, and for US electric hp multiply by 1.34048.

How do I convert watts to horsepower?

Divide watts by 745.7 for mechanical horsepower, or by 735.5 for metric horsepower (PS). So 1500 W is about 2.0 mechanical hp (1500 ÷ 745.7) or 2.04 PS (1500 ÷ 735.5).

How do I convert horsepower to kilowatts?

Multiply mechanical horsepower by 0.7457, since 1 hp is 745.7 W — so a 200 hp car is about 149 kW. For metric horsepower (PS) multiply by 0.7355 instead, and for a US electric-motor hp multiply by 0.746.

How do I convert PS to kW?

Multiply PS by 0.7355, since 1 PS is the metric horsepower of 735.5 W. So 510 PS is about 375 kW. If the number is actually US mechanical hp, multiply by 0.7457 instead — 510 hp then works out to 380 kW, a 5 kW difference from the same nominal figure.

What is 12,000 BTU/h in kilowatts?

About 3.52 kW. That is the classic "1-ton" air-conditioner rating — the cooling power that melts one short ton of ice in a day. A 24,000 BTU/h unit is a 2-ton AC near 7 kW, and 36,000 BTU/h is a 3-ton at roughly 10.5 kW, so the BTU/h figure tells you what floor area a unit can handle.

How many BTU per hour is one kilowatt?

One kilowatt is 3412.14 BTU/h, because 1 W is 3.41214 BTU/h. Installers round this to "1 kW is about 3.4 kBTU/h." Going the other way, 1 BTU/h is about 0.293 W.

Is my air conditioner's BTU rating power or energy?

It is power — a rate of heat flow, not a stored amount. A BTU per hour (BTU/h) is how fast the unit moves heat, which is why it converts to watts and kilowatts. A plain BTU with no "per hour" would be energy. Note the BTU/h rating is the heat moved, not the electricity drawn, so it is not the same as the unit's wattage.

Why is electric horsepower exactly 746 watts?

US electrical standards round the horsepower to a clean 746 W so motor math stays tidy — a 100 hp electric motor is then exactly 74.6 kW on its nameplate. That is about 0.04% above the mechanical horsepower of 745.7 W, which keeps its awkward decimal because it is tied to the foot, the pound and standard gravity.

What does PS mean, and where is it used?

PS stands for Pferdestärke, German for "horse strength." It is the metric horsepower — 735.5 W — and the same unit shows up as CV in Spain, France and Italy, ch in France, and 馬力 in Japan. Almost every non-US, non-UK car spec quotes power in PS or its local name, while US and UK specs use mechanical hp.

Is power the same thing as energy?

No. Power is a rate — the watt is one joule per second — while energy is an amount, like a watt-hour or kilowatt-hour. A 2 kW heater has a power of 2 kW; run it for three hours and it uses 6 kWh of energy. This tool converts power only; for joules, kWh or calories, use an energy converter.

How accurate is this power converter?

It uses the standard defined factors: mechanical hp at 745.7 W, metric hp (PS) at 735.5 W, electric hp at 746 W, and 1 kW at 1.34102 hp. The SI units and horsepower values are fixed by definition; only BTU/h and kcal/h carry a non-terminating decimal, so the rounding you see comes from how many places you choose to display.

Is this power converter free to use?

Yes, with no sign-up and nothing to install — it runs in your browser. Every power unit sits on one page, from watts and kilowatts to the three horsepowers, BTU/h and kilocalories per hour, so you can move between car specs, HVAC ratings and motor nameplates without switching tools. An embeddable version is available for automotive and engineering sites.

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