Engineering Unit Converter
Horsepower to Watts Calculator
Convert Mechanical, Electrical, Metric, Boiler, and other horsepower units to Watts and Kilowatts — with motor input power, current, and loss estimates.
Convert
Only use a custom factor when you know the applicable standard — it overrides all built-in conversions.
Result
1 mechanical horsepower is equal to approximately 745.70 watts, or 0.7457 kilowatts.
Horsepower Standards Compared
Different sites show different HP-to-watt values because horsepower has several historical definitions. Enter a value once and see how each standard treats it.
| Horsepower Type | Watts per HP | Typical Application |
|---|
Boiler horsepower is a steam-evaporation convention, not a mechanical shaft rating — that's why it's dramatically larger per "HP" than the others.
Motor Power Estimator Advanced
A motor's HP rating describes mechanical shaft output, not electrical input. Because of winding, core, friction, and stray-load losses, the electrical input power is always higher than the mechanical output.
Exact Unit Conversion
Engineering Estimate
| Efficiency | Mechanical Output | Estimated Electrical Input | Loss |
|---|
HP to Watts Reference Table
Generated from the mechanical horsepower factor (1 hp = 745.699872 W). Scroll on small screens.
| Horsepower | Watts | Kilowatts |
|---|
Common Motor HP Reference
Mechanical output only. Current isn't shown here because it depends on voltage, phase, power factor, and efficiency — use the Motor Power Estimator above for that.
| HP | Mechanical Watts | kW Output |
|---|
Generate a Custom HP Conversion Table
| Horsepower | Watts | Kilowatts |
|---|
Compare Motors
Compare mechanical output across up to three horsepower ratings (mechanical HP).
| Motor | HP | Mechanical kW | Relative to Motor A |
|---|
Formula Reference
"Exact" rows are defined unit conversions. "Estimate" rows are engineering approximations that depend on real-world motor conditions — never mix the two as though they carry the same certainty.
How Horsepower to Watts Conversion Works
Watts are the SI unit of power; horsepower is an older unit with several competing historical definitions. For mechanical horsepower, 1 hp equals 745.6998716 watts, so any mechanical horsepower value converts to watts by multiplying by that factor. The 746 W/HP figure many sites quote is simply a convenient rounding of that same number — and it happens to also match the separately-defined electrical horsepower convention, which is why it's so common.
Horsepower and Kilowatts Are Both Units of Power
Horsepower is not automatically an electrical measurement. A motor nameplate rated in HP is describing mechanical shaft output — what comes out the drive end. The electrical power going into the motor is higher, because some energy is lost to winding resistance, core losses, friction, windage, and stray-load losses. That's the entire reason the Motor Power Estimator above separates "exact conversion" from "engineering estimate."
Where This Conversion Is Used
Common Conversion Mistakes
- Assuming every HP definition is identical. Mechanical, metric, and boiler horsepower are not the same watt value.
- Treating motor HP as electrical input. It usually describes shaft output, not what the motor draws from the supply.
- Ignoring efficiency. Real electrical input is always higher than the mechanical output for a real motor.
- Using 746 as a universal constant. It's a useful rounding for mechanical/electrical HP, not for metric or boiler HP.
- Calculating current from HP alone. You also need voltage, phase, efficiency, and power factor.
- Sizing cable or breakers from calculated current alone. Final protection and conductor selection must follow the applicable electrical code and manufacturer data.
Frequently Asked Questions
How many watts are in one horsepower?
For mechanical horsepower, 1 hp ≈ 745.7 W, commonly rounded to 746 W.
Is 1 HP exactly 746 W?
Not for every definition. Mechanical horsepower is about 745.7 W; electrical horsepower is conventionally defined as exactly 746 W; metric horsepower is about 735.5 W.
How many kW is 1 HP?
For mechanical horsepower, 1 hp ≈ 0.7457 kW.
Is a 1 HP motor equal to 746 W of electrical consumption?
Not necessarily. 746 W (or 745.7 W) describes the mechanical output rating. Electrical input is higher and depends on the motor's efficiency.
How do I convert kW to HP?
For mechanical horsepower: HP = kW ÷ 0.745699872.
Why is metric horsepower different?
Metric horsepower (PS) comes from a different historical definition, roughly equal to 735.5 W, and is common on European engine and equipment ratings.
Can this calculator determine motor amps?
Yes, once you supply voltage, phase, power factor, and efficiency in Motor Power Estimator — but treat the result as an estimate. Manufacturer nameplate data and applicable code tables remain the reference for final equipment and conductor sizing.
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Engineering Disclaimer: This calculator provides unit conversions and preliminary engineering estimates. Motor current, efficiency, protection, conductor sizing, equipment selection, and installation requirements should be verified using the motor nameplate, manufacturer documentation, applicable electrical standards, and local electrical codes before final design or installation.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| P(W) | Power in watts | W |
| HP | Power in horsepower | hp |
| 746 | Conversion factor (1 hp = 746 W) | dimensionless |
What it means
One mechanical horsepower (HP) is defined as exactly 746 watts. The conversion is P(W) = HP × 746. This is commonly used for motor ratings in the US and other countries. Example: A 2 HP motor has an equivalent electrical power of 2 × 746 = 1492 W. When specifying power supplies or generators, it’s important to account for this value and also consider the motor efficiency and power factor. Understanding this conversion helps in selecting appropriate electrical equipment for motor loads.
Worked example
HP to Watts – Practical Example
Real‑World| Parameter | Value |
|---|---|
| HP | 5 |
| Formula | P(W) = HP × 746 |
Applications
Horsepower to watts conversion: P(W) = HP × 746 is used to convert between mechanical horsepower and electrical watts. Engineers use it to size motors, to compare power ratings, and to perform energy calculations. This conversion is essential for motor and drive selection.
- Motor power rating conversion for electrical design
- Comparison of mechanical and electrical power
- System efficiency and load calculations
- Energy consumption estimation
- Educational understanding of power units
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