Horsepower to Watts
Convert horsepower to watts with the exact factor (1 hp = 745.7 W), a quick reference table, and common motor and appliance ratings.
hp to W formula
To convert mechanical horsepower (hp) to watts (W), multiply by 745.7. One horsepower is defined as exactly 745.7 watts.
Quick reference: hp to W
Common values
1 hp = 745.7 W
5 hp = 3728.5 W
10 hp = 7457 W
100 hp = 74570 W
Worked example
Convert 1 hp to watts:
1 hp × 745.7 = 745.7 W
So 1 horsepower is 745.7 watts.
Why convert hp to W?
US engines are rated in horsepower, while electrical power is measured in watts or kilowatts internationally. This conversion makes the ratings comparable.
You can also use our calculator or read the paired guide W reference.
Frequently Asked Questions
How many watts are in a horsepower?
1 mechanical hp = 745.7 W.
How do I convert 5 hp to watts?
5 hp × 745.7 = 3728.5 W (about 3.73 kW).
Is HP the same as kW?
No. 1 hp = 0.7457 kW, so horsepower is the smaller unit.
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Quick Summary
hp to W uses a single exact factor. Use the formula above or the reference table for quick, accurate results.
Related Guide
Watts to HP: Electric Motor and Tool Power for US Buyers
Convert watts to hp for US electric motors, shop tools, and appliances. 1 watt equals 0.00134102 hp, and 1 mechanical horsepower equals 745.7 watts.
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HP to KW: Converting Horsepower to Kilowatts for US Cars and EVs
Convert hp to kw for US car specs, truck ratings, and EV motors. 1 mechanical horsepower equals 0.7457 kW, the standard American automakers use.
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Convert btu to kwh to estimate air conditioner energy use and cost. 1 BTU equals 0.000293071 kWh, so a 12000 BTU window AC uses about 3.52 kWh per hour.
Kilowatts to Horsepower
Convert kilowatts to horsepower with the exact factor (1 kW = 1.34102 hp), a quick reference table, and common engine and motor ratings.
kWh to BTU
Convert kilowatt-hours to BTU with the exact factor (1 kWh = 3412.14 BTU), a quick reference table, and common energy-use examples.
What Is a BTU? British Thermal Unit Explained
The BTU is the energy needed to raise one pound of water by one degree Fahrenheit. Learn how it sizes furnaces and AC units, and how it links to kWh and joules.
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Disclaimer
Unit conversions on this site use internationally recognized, fixed conversion factors (for example, 1 inch = 2.54 cm, 1 pound = 0.45359237 kg, 1 °F = (°C × 9/5) + 32). They are provided for general, informational, and educational use. For applications where accuracy is critical — such as medical dosing, engineering, scientific research, trade, or legal compliance — always verify results against authoritative sources such as the U.S. National Institute of Standards and Technology (NIST) and the official International System of Units (SI) brochure, and follow any applicable local standards.
Exact Constants & Authoritative Sources
Every conversion on this page uses the fixed, internationally agreed constants below — drawn from NIST and the SI Brochure. No values are estimated or rounded as if exact. See the full list on our Sources & Standards page.
- EXACT1 mechanical horsepower (hp) = 745.6998715823 watts (exact, 550 ft·lbf/s)
- EXACT1 British thermal unit, IT (Btu) = 1055.05585262 joules (exact)
- EXACT1 Btu/h = 0.293071070172 watts (exact, Btu ÷ 3600 s)
- EXACT1 watt (W) = 1 joule per second (definition)
Common Pitfalls & How to Avoid Them
Mechanical hp vs. metric hp
Mechanical hp = 745.7 W. Metric (PS) hp = 735.5 W and electrical hp = 746 W. Engine specs may use any of these; always check which.
Btu IT vs. thermochemical
UnitFig uses the IT Btu (1055.05585262 J). The thermochemical Btu (1054.35 J) is ~0.07% smaller and used in some chemistry contexts — keep them separate.
A unit-conversion reference site has no manufacturer-specific or device calibration parameters, so "layered tuning" does not apply here. The only real error-handling is input validation: the converter rejects non-numeric, empty, or out-of-range entries and shows a clear message, then falls back to exact constants above. No estimated or rounded figures are ever presented as exact.
Authoritative sources for this page
- NIST (U.S. National Institute of Standards and Technology) — NIST SP 330 — The International System of Units (SI), 2019 edition
- BIPM (International Bureau of Weights and Measures) — SI Brochure — The International System of Units (9th edition)
Last Updated 2026 | This article was reviewed for accuracy