How to Convert Watts to Horsepower
Converting watts to horsepower is the universal bridge between electrical and mechanical power — it's how you translate a 750 W electric motor rating into a 1 HP equivalent for a compressor, how a 2,200 W EV onboard charger maps to ~3 HP of charging power, and how a 300 W servo motor stacks up against a fractional-HP induction motor. 1 mechanical horsepower = 745.7 watts. Divide watts by 745.7 (or multiply by 0.001341). The distinction matters: metric horsepower (PS/CV) uses 735.5 W, and electrical horsepower uses exactly 746 W. This conversion is critical in HVAC (a 3,728 W compressor = 5 HP), in electric vehicle design (a Tesla Model 3 motor rated at 211,000 W = 283 HP), and in consumer appliances (a 1,200 W microwave draws 1.61 HP of electrical power — more than many small lawnmower engines).
The Conversion Formula
HP = W ÷ 745.7 (mechanical)
Worked Examples
Example 1: Convert 1,500 W to HP
1,500 ÷ 745.7 = 2.01 HP (a typical 1.5 kW bench grinder motor)
Example 2: Convert 746 W to HP
746 ÷ 745.7 = 1.0004 HP (essentially 1 HP — the electrical HP definition)
Example 3: Convert 75,000 W to HP
75,000 ÷ 745.7 = 100.6 HP (a small economy car engine)
Common Watts to HP Conversions
| Watts | HP |
|---|---|
| 373 W | 0.5 HP |
| 746 W | 1 HP |
| 1,500 W | 2.01 HP |
| 3,728 W | 5 HP |
| 7,457 W | 10 HP |
| 75,000 W | 100.6 HP |
Related Unit Converters
Frequently Asked Questions
How do I convert watts to horsepower?
Divide watts by 745.7 (mechanical HP). Formula: HP = W ÷ 745.7. For metric HP (PS), divide by 735.5. For electrical HP, divide by exactly 746.
How many watts in 1 HP?
1 mechanical HP = 745.7 watts. This is the standard used for internal combustion engines in the US and UK. An electric motor labeled "1 HP" typically draws 746 W of electrical input power — the 0.3 W difference is a rounding convention, not a measurement discrepancy.
Why is engine HP different from electrical motor HP?
Engine HP is measured as brake horsepower (bhp) at the crankshaft, with conversion 1 bhp = 745.7 W. Electric motor HP is the mechanical output power, while the nameplate may show input watts. Motor efficiency (~85-95%) means a "1 HP" motor actually consumes ~870 W of electricity to deliver 746 W of shaft power.
Engineering Context
The watt-to-horsepower conversion underpins the electrification of everything formerly powered by combustion. A Tesla Model 3 Long Range has a rear motor rated at 211 kW (283 HP) and a front motor at 147 kW (197 HP) — together 358 kW (480 HP). But unlike a 480 HP V8 that only hits peak power at 6,000 RPM for a fraction of a second, the EV delivers peak torque from 0 RPM. This is why a 283 HP EV can out-accelerate a 350 HP gasoline car: area under the power curve matters more than the peak number. In data centers, a server rack rated at 8 kW (10.7 HP) of electrical input requires ~3 tons of cooling capacity (1 ton = 12,000 BTU/hr = 3.517 kW). The ASHRAE TC 9.9 guidelines express data center power density in W/sq ft, but facility chillers are sized in HP — the W-to-HP conversion is embedded in every cooling load calculation. A Liebert XD 30-ton chiller compressor draws 28 kW (37.5 HP), and the condenser fans add another 5.6 kW (7.5 HP). In aviation, the Rolls-Royce Trent XWB turbofan produces 97,000 lbf of thrust at takeoff, but its core generates ~50,000 shp (37,300,000 W) — the conversion to watts simplifies comparison with the GE9X's 60,000 shp (44,700,000 W) core. The James Watt story itself is engineering economics: Watt defined 1 HP as 33,000 ft·lbf/min after observing that a mine pony could lift 220 lb of coal 100 ft in one minute (22,000 ft·lbf/min), then adding a 50% safety margin to ensure his steam engines would never be undersold against horses.
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