HP ↔ kW Converter
1 mechanical horsepower = 0.745699872 kW
One mechanical horsepower equals 0.7457 kilowatts. That single fact answers most HP-to-kW questions, but it hides a problem: there are four different types of horsepower, and each one converts to a different kW value. Use the wrong conversion factor and your motor calculation, generator sizing, or vehicle comparison will be off.
This guide gives you the exact formula for each HP type, a worked conversion table from 1 to 500 HP, and practical examples from cars, electric motors, and industrial equipment.
The HP to kW Formula
For mechanical (imperial) horsepower, the formula is:
kW = HP × 0.7457
To go the other way:
HP = kW ÷ 0.7457
That conversion factor comes directly from the physics definition of a horsepower. James Watt measured that one horse could sustain a work rate of 550 foot-pounds per second. That equals 745.7 watts, or 0.7457 kW.
Three worked examples using this formula:
- 150 HP engine: 150 × 0.7457 = 111.9 kW
- 250 HP engine: 250 × 0.7457 = 186.4 kW
- 500 HP engine: 500 × 0.7457 = 372.9 kW
Four Types of Horsepower and Their kW Values
The confusion around HP-to-kW conversion usually comes from one source: the word “horsepower” does not refer to a single unit. Four distinct definitions exist, each with a different watt value.
Mechanical Horsepower (HP or hp)
The standard in the United States and United Kingdom. Defined as exactly 550 foot-pounds per second, which equals 745.699872 watts. This is the type used in car engine ratings across North America and in most engineering calculations.
1 mechanical HP = 0.7457 kW
Metric Horsepower (PS or CV)
Used across Europe, Japan, and much of Asia. Called Pferdestärke in German (PS) and chevaux-vapeur in French (CV). Defined as the power needed to lift 75 kilograms one metre in one second, which equals exactly 735.49875 watts. European car specs list PS or CV, not mechanical HP.
1 metric HP (PS) = 0.7355 kW
The difference between mechanical and metric HP is about 1.4%. A car rated at 200 PS produces 147.1 kW, while 200 mechanical HP produces 149.1 kW. Small but real.
Electrical Horsepower
Used specifically for electric motors and HVAC equipment ratings. Defined as exactly 746 watts — slightly higher than mechanical HP.
1 electrical HP = 0.746 kW
Boiler Horsepower
A completely different unit used in steam systems. One boiler horsepower is the energy needed to evaporate 34.5 pounds of water per hour at 212°F (100°C), which equals 9,809.5 watts. This is over 13 times larger than a mechanical horsepower. Boiler HP appears only on steam boiler nameplates and industrial heating systems.
1 boiler HP = 9.81 kW
| HP Type | Watts | kW | Where Used |
|---|---|---|---|
| Mechanical (imperial) | 745.7 W | 0.7457 kW | US, UK car engines, general engineering |
| Metric (PS / CV) | 735.5 W | 0.7355 kW | Europe, Japan, Asia car ratings |
| Electrical | 746 W | 0.746 kW | Electric motors, HVAC equipment |
| Boiler | 9,809.5 W | 9.81 kW | Steam boilers, industrial heating |
HP to kW Conversion Table
All values below use mechanical horsepower (0.7457 kW per HP). For metric HP, multiply the HP value by 0.7355 instead.
| Horsepower (HP) | Kilowatts (kW) |
|---|---|
| 1 HP | 0.75 kW |
| 5 HP | 3.73 kW |
| 10 HP | 7.46 kW |
| 15 HP | 11.19 kW |
| 20 HP | 14.91 kW |
| 25 HP | 18.64 kW |
| 30 HP | 22.37 kW |
| 40 HP | 29.83 kW |
| 50 HP | 37.28 kW |
| 60 HP | 44.74 kW |
| 75 HP | 55.93 kW |
| 100 HP | 74.57 kW |
| 125 HP | 93.21 kW |
| 150 HP | 111.86 kW |
| 200 HP | 149.14 kW |
| 250 HP | 186.42 kW |
| 300 HP | 223.71 kW |
| 400 HP | 298.28 kW |
| 500 HP | 372.85 kW |
kW to HP: Reverse Conversion
To convert kilowatts back to mechanical horsepower:
HP = kW ÷ 0.7457
Or equivalently:
HP = kW × 1.341
Common kW-to-HP values:
| Kilowatts (kW) | Horsepower (HP) |
|---|---|
| 1 kW | 1.34 HP |
| 10 kW | 13.41 HP |
| 50 kW | 67.05 HP |
| 75 kW | 100.6 HP |
| 100 kW | 134.1 HP |
| 150 kW | 201.2 HP |
| 200 kW | 268.2 HP |
| 300 kW | 402.3 HP |
| 500 kW | 670.5 HP |
Real-World Examples
Cars
North American car specs use mechanical HP. European and Japanese specs use PS (metric HP). When you compare a US and European car review of the same model, the numbers differ slightly for this reason.
- A compact car with 130 HP produces about 96.9 kW
- A mid-size car with 200 HP produces about 149.1 kW
- A sports car with 400 HP produces about 298.3 kW
- The Hyundai Kona EV: rated at 150 kW, which equals 201.2 HP
Industrial Motors
Electric motors in factories, pumps, and compressors are often nameplate-rated in HP in the US, while the rest of the world uses kW. Converting between them is a daily task for maintenance engineers.
- A 5 HP pump motor: 5 × 0.7457 = 3.73 kW
- A 25 HP air compressor: 25 × 0.7457 = 18.64 kW
- A 100 HP industrial motor: 100 × 0.7457 = 74.57 kW
HVAC Systems
Air conditioning and heat pump equipment in the US is rated in tons for cooling capacity and HP for the compressor motor. Electrical HP (0.746 kW) is the standard here. A 5 HP HVAC compressor draws approximately 5 × 0.746 = 3.73 kW of electrical power at the motor shaft under ideal conditions.
Generators
Generator output is rated in kW for the electrical side. The engine driving the generator is rated in HP. A common 10 kW standby generator uses an engine of roughly 18 to 20 HP to produce that output, because mechanical-to-electrical conversion losses mean the engine must produce more mechanical power than the electrical output.
HP to kW for Electric Motors: Why Efficiency Matters
The formula kW = HP × 0.7457 gives you the mechanical output power at the motor shaft. It does not tell you how much electricity the motor actually consumes from the supply. For that, you need to account for motor efficiency.
The real-world formula for electrical input power is:
kW (input) = (HP × 0.7457) ÷ efficiency
Standard NEMA electric motors run at 85 to 95% efficiency. Premium efficiency (IE3) motors reach 93 to 96%.
Example: a 10 HP motor at 90% efficiency
- Shaft output: 10 × 0.7457 = 7.46 kW
- Electrical input: 7.46 ÷ 0.90 = 8.29 kW
That 0.83 kW difference is the power lost as heat inside the motor. On a motor running 8,000 hours per year at $0.12/kWh, that loss costs about $796 per year. Across a fleet of motors in a manufacturing plant, efficiency differences between motor grades become a significant budget line.
A common mistake in generator sizing is using the basic HP-to-kW formula without efficiency. The generator must supply the electrical input power, not the mechanical output. Undersizing a generator by ignoring efficiency causes voltage drops, overheating, and failed motor starts.
Why Electric Vehicles Use kW Instead of HP
Electric motors are rated in kilowatts because kW is the SI unit for power and maps directly to the electrical supply they draw from. Measuring an electric motor in HP is technically valid but roundabout — it requires converting from an electrical unit to a mechanical-era unit and then back.
As EV adoption grows, the automotive industry is shifting. Australia, for example, already uses kW as the standard for all vehicle power ratings, petrol or electric. Most EV manufacturers now list both units: the Hyundai Kona EV nameplate reads 150 kW / 201 hp. The BMW iX3 is rated at 210 kW / 286 hp. The Tesla Model 3 Long Range produces 366 kW / 491 hp at peak output.
One practical difference between petrol and electric power ratings: a petrol engine reaches peak HP at a specific RPM, typically between 5,500 and 7,000 RPM. An electric motor delivers peak torque from zero RPM. A 150 kW EV motor and a 150 kW petrol engine on paper have the same peak power but behave differently — the EV feels faster off the line because full torque is available the moment you press the accelerator.
The most powerful production EVs in 2025 put the HP-to-kW relationship in perspective: the Rimac Nevera R produces 1,571 kW, which converts to 2,106 HP. That is more mechanical horsepower than almost any production combustion car in history, generated with no gear changes and full torque from standstill.
Where Horsepower Came From
James Watt coined the term in the late 18th century to sell steam engines to mine operators. Mine owners used horses to pump water out of shafts. Watt measured how much work a horse could sustain — he calculated 33,000 foot-pounds per minute — and used that number to describe how many horses each engine could replace. An engine rated at 10 HP could do the work of ten horses.
The unit spread globally because steam engines spread globally. When internal combustion engines replaced steam, they inherited the horsepower rating system. When electric motors arrived, manufacturers continued using HP to give buyers a familiar point of comparison. The unit is now embedded in consumer expectations even though the underlying physics of modern engines has nothing to do with horses.
The kilowatt was proposed in 1882 by Sir Charles William Siemens and formally adopted in 1908. It is the SI-standard unit for power. Every scientific and engineering discipline outside automotive sales uses watts and kilowatts. Horsepower survives in consumer contexts largely because of habit and because switching units would confuse buyers who have spent decades comparing cars in HP.
Frequently Asked Questions
How do you convert HP to kW?
Multiply the horsepower value by 0.7457. For example, 100 HP equals 74.57 kW. This formula applies to mechanical (imperial) horsepower. For metric horsepower (PS), multiply by 0.7355 instead.
Is 1 HP equal to 1 kW?
No. One mechanical horsepower equals 0.7457 kW, or roughly three-quarters of a kilowatt. To get 1 kW, you need approximately 1.341 HP.
What is the difference between mechanical HP and metric HP?
Mechanical horsepower (used in the US and UK) equals 745.7 watts, or 0.7457 kW. Metric horsepower (called PS in Germany and Europe) equals 735.5 watts, or 0.7355 kW. The difference is small — about 1.4% — but it matters when comparing car specifications across regions.
How many HP is 100 kW?
100 kW equals approximately 134.1 mechanical horsepower. Divide the kW value by 0.7457 to get HP. A 100 kW electric motor is roughly equivalent to a 1.4-litre petrol engine in terms of peak power output.
Why do electric vehicles use kW instead of HP?
Electric motors are rated in kilowatts because kW is the standard SI unit for power and matches directly with the electrical systems that supply the motor. Horsepower was designed for mechanical engines running on fuel. As EVs become mainstream, kW is increasingly used for all vehicle types globally.
Does motor efficiency change the HP to kW calculation?
Yes, for real-world motor sizing. The basic formula (kW = HP × 0.7457) gives you the mechanical output power at the shaft. To find the electrical input power a motor actually draws, divide by efficiency: kW input = (HP × 0.7457) ÷ efficiency. A 10 HP motor at 90% efficiency draws about 8.29 kW of electricity from the supply, not 7.46 kW.
What is boiler horsepower in kW?
One boiler horsepower equals 9.81 kW. Boiler HP is a completely different unit from mechanical or metric HP. It measures a boiler’s capacity to convert water into steam, not mechanical output power. It appears only on steam boiler nameplates and industrial heating systems.
