Convert hp to kW horsepower ↔ kilowatts Free Online Secure
Type a value in horsepower and read it in kilowatts at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert hp to kW (horsepower ↔ kilowatts)
| hp | kW |
|---|---|
| 1 | 0.74569987158227022 |
| 2 | 1.49139974316454044 |
| 3 | 2.23709961474681066 |
| 5 | 3.7284993579113511 |
| 10 | 7.4569987158227022 |
| 20 | 14.9139974316454044 |
| 50 | 37.284993579113511 |
| 100 | 74.569987158227022 |
Where these units come from
Horsepower is a sales figure that outlived its sales pitch. In the 1780s James Watt needed to tell mill owners what his steam engine was worth in the only terms they knew, so he measured what a horse could haul and rounded it to 33,000 foot-pounds a minute. The watt was named after him a century later and is the SI unit, defined with no animals involved: one joule every second. The two have never quite agreed, and Europe added a third — metric horsepower, the PS or CV that European engines are rated in, which is about 1.4% smaller than the mechanical horsepower used on this page.
Where you meet them
Watts and kilowatts measure everything that consumes or produces power: kettles, motors, heat pumps, solar panels, amplifiers, data centres. Horsepower survives almost entirely in engines — cars, boats, tractors and outboards — where it is less a measurement than a way of talking. Electric cars have put the two side by side on the same spec sheet, which is where most people now notice that one number has to be converted into the other.
Questions people ask
Which horsepower does this page use?
Mechanical horsepower, 550 foot-pounds per second, which works out to about 745.7 watts. European engines are usually rated in metric horsepower — written PS, CV, ch or pk — which is 735.49875 watts exactly, roughly 1.4% smaller. A car advertised as 150 PS is about 148 mechanical hp. The difference is small but it is not rounding, and it always flatters the metric figure.
Why are kettles in watts and car engines in horsepower?
Only habit. They are the same quantity, and a 2 kW kettle and a 2.7 hp kettle would be the same appliance. Electricity arrived already metric and was never named after a horse; engines arrived with Watt's own sales figure attached and kept it. The conversion is exact in the sense that the definition is fixed — nothing is measured at the point of conversion.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Horsepower to kilowatts: which horsepower is on the data plate?
Engines, motors and pumps made for the American market are rated in horsepower, while most of the rest of the world uses kilowatts. The trouble is that "horsepower" has been defined in several ways: the mechanical horsepower of 745.7 W, the metric horsepower of 735.5 W, the electrical horsepower of exactly 746 W and the boiler horsepower of 9,810 W. To convert hp to kW, multiply by 0.7457: 10 hp is 7.46 kW, 100 hp is 74.6 kW and 500 hp is 372.8 kW. The calculator above multiplies as you type, and the sections below show how engine ratings, motor frames and test standards turn horsepower into something you can compare.
The page gives the rule with worked examples, a profile of each unit, a comparison and a long run of engine, motor and vehicle cases, followed by the usual slips. The calculation runs in your browser and nothing you type is sent anywhere. For approvals and insurance, use the power stated on the official documents.
How to convert hp to kW: multiply by 0.7457
The rule
One mechanical horsepower is 550 foot-pounds per second, which is 745.6999 watts. To convert hp to kW, multiply the horsepower by 0.7457: 25 hp gives 18.6 kW, 175 hp gives 130.5 kW and 600 hp gives 447.4 kW. To go the other way, multiply kW by 1.341.
Worked examples
An outboard motor of 115 hp delivers 85.8 kW. A garden tractor of 21 hp delivers 15.7 kW. A farm tractor of 150 hp delivers 111.9 kW, and a pump motor of 10 hp 7.46 kW.
The other horsepowers
A metric horsepower, PS or CV, is 735.5 W, so 100 PS is 73.55 kW against 74.57 kW for 100 hp. The electrical horsepower on a motor plate is 746 W, which differs from the mechanical one by 0.04 per cent. A boiler horsepower is 9,810 W, 13.2 hp, and belongs to steam plant.
A quick sanity test
The answer in kW is about a quarter smaller than the horsepower figure. If a “convert hp to kW” calculation gave a larger number than you started with, you multiplied by 1.341 instead of 0.7457.
Horsepower
The American unit of engine power
James Watt introduced the unit around 1780 to compare steam engines with the draught horses they replaced. Today it is fixed at 33,000 foot-pounds per minute. It remains the standard rating for cars, outboards, pumps and tools in the United States.
Where it appears
Vehicle and engine specifications, motor plates and equipment catalogues.
The kilowatt
The SI unit of power
The kilowatt is a thousand watts. It is the unit in which type-approval, tax and grid rules in most of the world state power, and the unit in which electric motors, batteries and chargers are rated.
Where it appears
Registration papers, licence categories, electric drivetrains and standards.
Horsepower against kilowatts
One horsepower is 0.7457 kW, so a figure in kW is a quarter smaller than the same power in hp. 200 hp is 149.1 kW and 1,000 hp is 745.7 kW. Both describe identical power; only the scale differs.
The conversion is exact. The commonest trap is confusing mechanical horsepower with the metric kind, which differ by 1.4 per cent.
Where the conversion shows up
Torque and rpm
Horsepower equals torque in pound-feet times rpm divided by 5,252. An engine making 400 lb·ft at 4,000 rpm is therefore producing 304.7 hp. In metric terms it is 542 N·m at 4,000 rpm; kW equals N·m times rpm over 9,549, giving 227.2 kW. A “convert hp to kW” calculation agrees with both routes.
Fuel use
Engine fuel consumption is quoted in pounds per horsepower-hour. A petrol engine at 0.45 lb/hp·h uses 274 g per kWh, and a diesel at 0.35 lb/hp·h uses 213 g per kWh. At 100 kW that is 27 and 21 kg of fuel per hour.
Motor plates
A three-phase motor imported from the United States and marked 10 hp has 7.46 kW at the shaft, which matches the European standard rating of 7.5 kW. The two are close in power but differ in frame size, voltage and frequency.
SAE gross, SAE net and DIN
Until the early 1970s, American makers quoted gross power, measured without fan, exhaust and alternator, and then switched to net. A "gross" 400 hp could be a net 320 hp, which is 239 kW. The German DIN standard measures net power in PS. When you convert hp to kW, check the standard behind the number.
Motorcycles
A touring cruiser of 90 hp makes 67.1 kW and a sports bike of 200 hp 149.1 kW. European licence categories use kW, so a 35 kW limit equals 46.9 hp. A “convert hp to kW” calculation tells a rider which American models fit the category.
Ships and big engines
A large container ship may have 100,000 hp of propulsion, which is 74.6 MW. A tugboat of 4,000 hp has 2.98 MW. A diesel locomotive of 4,400 hp has 3.28 MW. These ratings appear in horsepower in some regions and in megawatts in others.
Lawn mowers and small engines
Small engines carry gross ratings of 3 to 25 hp. A 21 hp riding mower is 15.7 kW on paper, while the engine's net output under the SAE J1940 procedure is lower, often by 10 to 20 per cent. Labels usually say whether the figure is gross or net, and the kW value tells you the order of magnitude only.
Peak horsepower on vacuums
Shop vacuums claim "6.5 peak hp", which is 4.85 kW. A 15 A outlet at 120 V can supply only 1,800 W, which is 2.4 hp. Peak horsepower is computed from the stall torque of the motor, not from what it can sustain, and no household vacuum delivers it.
Pumps and water horsepower
Water horsepower is the hydraulic output: flow times head times density. A pump delivering 100 cubic metres an hour against 20 metres is giving 5.45 kW, 7.3 hp. With a pump efficiency of 65 per cent, the shaft must supply 8.4 kW, 11.2 hp.
Compressors
An air compressor of 5 hp has 3.73 kW. Its delivery is rated in cubic feet per minute at a pressure, for instance 18 CFM at 90 psi, which is 8.5 litres per second at 6.2 bar. The shaft power sets the delivery, and a “convert hp to kW” calculation makes sizing against a European supply easier.
Pickup trucks and heavy vehicles
A full-size pickup at 400 hp has 298 kW, a heavy-duty diesel pickup at 475 hp has 354 kW and a semi-trailer tractor at 500 hp has 373 kW. Power divided by mass says more about acceleration: 298 kW over 2.3 tonnes is 130 kW per tonne.
Electric vehicles quoted in hp
Electric cars sold in America carry horsepower figures too. A car with 283 hp has 211 kW, and one with 670 hp has 500 kW. Since electric motors give full torque at standstill, the continuous figure may be well below the peak, and the kW quoted for approval is usually the 30-minute rating.
Racing figures
A hypercar of 1,000 hp has 745.7 kW and a top-class racing prototype of 700 hp has 522 kW. Press reports use hp, regulations use kW, and a “convert hp to kW” calculation brings the two together.
A worked example
You compare a 285 hp American SUV with a European one of 220 kW. The American one is 212.5 kW, so it is 7.5 kW or 3.4 per cent weaker on paper. If the American number is a gross rating and the European one is net, the gap may reverse, so check the standard before concluding.
Brake, shaft and wheel horsepower
Brake horsepower (bhp) is measured at the crankshaft, shaft horsepower (shp) at an output shaft, and wheel horsepower (whp) on a chassis dynamometer. The wheels get 10 to 15 per cent less. A car at 300 bhp may show 255 to 270 whp, 190 to 201 kW at the wheels.
The mental shortcut
To convert hp to kW in your head, take three quarters of the horsepower. For 200 hp: three quarters is 150 kW, against the exact 149.1. The error is 0.6 per cent. For a closer figure subtract a further 0.6 per cent of the answer.
Spreadsheet formulas
In a spreadsheet, keep the hp in column A and use =A2*0.7456999 in column B. For metric horsepower use =A2*0.73549875. The reverse is =B2*1.341022. A column that multiplies hp by 745.7 gives watts and offers a quick cross-check.
Rounding in specifications
Engine power is quoted to the nearest 5 or 10 hp, so give kW to the nearest 1. A 285 hp engine is 212.5 kW, not 212.5245. Extra digits imply a precision that the test, with its tolerance of a few per cent, does not have.
Landmarks to memorise
10 hp is 7.5 kW. 50 hp is 37.3 kW. 100 hp is 74.6 kW. 200 hp is 149 kW. 500 hp is 373 kW. 1,000 hp is 746 kW. With these landmarks nearly every mental convert hp to kW is possible.
Reference ladder
3 hp: 2.24 kW. 15 hp: 11.2 kW. 40 hp: 29.8 kW. 90 hp: 67.1 kW. 175 hp: 130.5 kW. 350 hp: 261 kW. 750 hp: 559 kW. A table like this lets you test a calculator output at a glance.
Checking by reversing
To check a “convert hp to kW” calculation result, multiply the answer by 1.341. If 90 hp gave 67.1 kW, then 67.1 × 1.341 = 90.0. A second test is size: the kW figure must lie just below three quarters of the horsepower.
Link to BTU per hour and watts
One horsepower is 745.7 W, 2,544 BTU/h, 642 kcal/h and 550 ft·lbf/s. An engine of 100 hp therefore corresponds to about 254,400 BTU/h of mechanical power. All of these describe the same rate, and a “convert hp to kW” calculation just swaps the label.
Two routes to one answer
You can multiply by 0.7457 straight, or go through watts: hp × 745.7 / 1,000. A third route uses foot-pounds per second: 550 ft·lbf/s × 1.3558 W per ft·lbf/s = 745.7 W. If the routes disagree, a digit was copied wrongly.
What the fuel supplies
An engine making 100 kW at 30 per cent efficiency takes 333 kW of heat from its fuel, which is 333 kWh each hour, about 36 litres of petrol. The power on the plate is therefore only a third of the energy flowing in. A 134 hp engine, the same 100 kW, is no more frugal than its kW figure implies.
Muscles, wind and water
A fit cyclist holds about 250 W for an hour, which is a third of a horsepower. Seven or eight such riders match one mechanical horsepower. A small wind turbine of 10 kW delivers 13.4 hp at its rated wind speed, and a micro-hydro set of 3 kW delivers just over 4 hp.
Matching IEC and NEMA motor sizes
European motors come in 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30 and 37 kW, while American ones come in 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40 and 50 hp. So 7.5 hp is 5.6 kW, near 5.5, and 15 hp is 11.2 kW, near 11. 20 hp (14.9 kW) fits 15, 25 hp (18.6 kW) fits 18.5, and 50 hp (37.3 kW) fits 37.
Power on the shaft and power drawn
A 5 hp motor delivers 3.73 kW at the shaft. At an efficiency of 88 per cent it draws 4.24 kW from the supply. Wire and breaker sizes depend on the electrical figure, not on the horsepower on the plate, so apply the efficiency before looking at a cable table.
Outboard motors
Small outboards are rated at the propeller shaft. A 9.9 hp motor is 7.4 kW, a 90 hp motor 67.1 kW and a 300 hp motor 223.7 kW. Boat-builders' maximum horsepower labels also use these ratings, so a European buyer must convert them before comparing with a rated limit in kW.
Tractors, PTO and engine ratings
A tractor of 200 hp at the engine may have only 170 to 180 hp at the power take-off, which is 127 to 134 kW. Tractor catalogues give both. Implements are matched to the PTO figure, so converting the right number matters more than converting accurately.
Tax horsepower
Some countries have used a formula that has little to do with real power. The old RAC rating in Britain was cylinder bore squared times the number of cylinders over 2.5, so four cylinders of 3 inches gave 14.4 hp. French fiscal horsepower and Italian fiscal ratings are other examples. None converts to kW with 0.7457.
Turboprops and shaft power
A turboprop rated at 1,000 shp has 745.7 kW at the propeller shaft, plus a small residual jet thrust. Makers sometimes quote equivalent shaft horsepower, which adds the jet thrust. Small turboprops of 600 to 750 shp put out 447 to 559 kW.
Light aircraft and helicopters
A piston aircraft engine of 200 hp has 149.1 kW at sea level and rated rpm. A light helicopter at 245 hp has 182.7 kW. Power drops about 3 per cent per 1,000 feet of altitude without a turbocharger, so the kW figure on the page is the best case.
More values for convert hp to kW
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 hp = 0.07457 kW
- 0.5 hp = 0.37285 kW
- 3 hp = 2.2371 kW
- 4 hp = 2.9828 kW
- 7 hp = 5.2199 kW
- 15 hp = 11.1855 kW
- 20 hp = 14.914 kW
- 75 hp = 55.9275 kW
- 200 hp = 149.14 kW
- 500 hp = 372.85 kW
- 2,000 hp = 1,491.4 kW
- 10,000 hp = 7,457 kW
Common slips with a “convert hp to kW” calculation
Using the wrong direction
From hp to kW the number gets smaller. If 150 hp became 201, you used the factor for the other direction.
Mixing hp and PS
100 PS is not 100 hp. For kW, the factor for PS is 0.7355 and for hp 0.7457. Check which unit the advert uses before you convert.
Taking peak for continuous
Peak or maximum horsepower is a short-term or theoretical rating. Compare continuous ratings in kW, and look at amps and volts for anything powered from a socket.
Short answers
How do I convert hp to kW?
Multiply the horsepower by 0.7457.
How many kW in 100 hp?
74.57 kW.
How many kW in 100 PS?
73.55 kW.
How many hp in 1 kW?
1.341 hp.
Does my number leave my device?
No, the calculation runs in your browser.
More pages and a wrap-up
For other power conversions see Convert hp to W, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C, Convert km/h to Mach, Convert °R to °C, Convert mm to cm, Convert L/100km to MPG (US). For the opposite direction see Convert kW to hp.
In short, a “convert hp to kW” calculation means one multiplication by 0.7457 and a unit written next to the result. Your figure is calculated locally, with no account and no upload.