Power converter guide
Power is the rate of energy transfer. The watt (W) is the SI derived unit equal to one joule per second, so this converter uses watts as its common base.
Horsepower is not one universal factor. Mechanical horsepower and metric horsepower are separate choices here. Thermal rates also identify the International Table BTU or thermochemical calorie convention.
How to convert power units
- Enter power: Enter a finite numeric rate in the selected source unit.
- Choose the convention: Select mechanical or metric horsepower explicitly when using horsepower.
- Choose the target: Select the output unit or reverse the pair with Swap.
- Convert: Select Convert power to calculate through watts.
Formula and variables
Every supported power unit is represented by its rate in watts.
target power = source power × (watts per source unit) ÷ (watts per target unit)- Pₛ — Source power
- The signed finite power value entered.
- fₛ — Source factor
- Watts represented by one source unit.
- fₜ — Target factor
- Watts represented by one target unit.
Convert mechanical horsepower to watts
Express one unit of mechanical horsepower in SI power.
- Amount
- 1
- From
- mechanical hp
- To
- W
- 1 mechanical hp × 745.6998715822702 W/hp
Result: 1 mechanical hp ≈ 745.699871582 W.
Metric horsepower would produce a different result, so the horsepower convention must remain attached.
Understanding your results
Power is a rate
A value in W or hp does not by itself state how much energy is used. Energy requires multiplying or integrating power over time.
Signed power
A negative sign can represent reverse flow, generation, or another chosen balance convention. The converter preserves but does not interpret that sign.
Assumptions
- One watt equals one joule per second.
- Mechanical horsepower equals 745.6998715822702 W.
- Metric horsepower equals 735.49875 W.
- BTU per hour uses the International Table BTU.
Limitations
- The calculator does not estimate energy consumption without a duration.
- It does not account for motor, generator, drivetrain, or thermal efficiency.
- Electrical power factor and phase are outside a unit-only conversion.
- Some industries use other horsepower or heat-unit conventions.
Common mistakes
- Confusing kW with kWh.
- Using an unspecified horsepower definition.
- Treating equipment input power and output power as equal.
- Using BTU as though it were already a per-hour power unit.
- Adding false precision to a rounded equipment rating.
Practical use cases
Motors and engines
Compare mechanical or metric horsepower ratings with W and kW while preserving the stated standard.
Heating and energy systems
Translate Btu_IT/h or thermochemical calorie rates to watts for a common rate basis.
Planning and decision guide
Separate rating from delivered output
Document whether the source figure is input, shaft output, electrical output, thermal output, or nameplate power. A unit conversion does not account for efficiency losses.
Frequently asked questions
How many watts are in one horsepower?
One mechanical horsepower is about 745.699871582 W. Metric horsepower is different at 735.49875 W.
Is kW the same as kWh?
No. kW is power; kWh is energy accumulated over time.
How many watts are in one Btu per hour?
Using the International Table BTU, 1 Btu_IT/h is about 0.293071070172 W.
Why are two horsepower units listed?
Mechanical and metric horsepower have different defined watt factors and cannot be treated as identical.
Can power be negative?
Yes in many sign conventions, such as export versus import. The converter retains the sign without assigning its meaning.
Sources and review
- NIST Guide to the SI, Appendix B.9: Factors for Units Listed by Kind of Quantity or Field of Science — National Institute of Standards and Technology. Accessed 2026-08-29.
- NIST Guide to the SI, Chapter 4: The Two Classes of SI Units and the SI Prefixes — National Institute of Standards and Technology. Accessed 2026-08-29.
Reviewed 2026-08-29.