Quick answer
Power units convert through watts. 1 mechanical horsepower equals 745.6999 W, and 1 kW is about 1.341 hp.
Enter a value and choose the units. The calculator returns the converted power.
Related tools: Power of 2 Calculator: Compute 2 raised to an integer power exactly. Power Calculator: Mechanical power from work and time, or force and velocity.
How to use the Power Converter
- Enter value.
- Choose from: Milliwatt (mW), Watt (W), Kilowatt (kW), Megawatt (MW), Gigawatt (GW) and Horsepower (mechanical) and 5 more.
- Choose to: Milliwatt (mW), Watt (W), Kilowatt (kW), Megawatt (MW), Gigawatt (GW) and Horsepower (mechanical) and 5 more.
- Enter decimal places (between 0 and 10). It starts at 4.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Value | A number | — |
| From | Choose one: Milliwatt (mW); Watt (W); Kilowatt (kW); Megawatt (MW); Gigawatt (GW); Horsepower (mechanical); Metric horsepower (PS); BTU per hour; … | Starts at Milliwatt (mW) |
| To | Choose one: Milliwatt (mW); Watt (W); Kilowatt (kW); Megawatt (MW); Gigawatt (GW); Horsepower (mechanical); Metric horsepower (PS); BTU per hour; … | Starts at Watt (W) |
| Decimal places | A number | ≥ 0, ≤ 10, starts at 4 |
Formula and method
Formula
result = value × (factor of source ÷ factor of target), base unit: watt
IEEE-754 double precision; displayed to the chosen number of decimal places (default 4). Very small or large results are shown in scientific notation.
Every unit is defined by an exact or published factor to the base unit (watt). The value is multiplied by the source factor and divided by the target factor.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Value = 1; From = Horsepower (mechanical); To = Watt (W); Decimal places = 4.
| Result | Value |
|---|---|
| Horsepower (mechanical) → Watt (W) | 745.6999 |
| Input | 1 Horsepower (mechanical) |
Example 2
Inputs: Value = 1; From = Kilowatt (kW); To = Watt (W); Decimal places = 4.
| Result | Value |
|---|---|
| Kilowatt (kW) → Watt (W) | 1,000 |
| Input | 1 Kilowatt (kW) |
Example 3
Inputs: Value = 1; From = Metric horsepower (PS); To = Watt (W); Decimal places = 5.
| Result | Value |
|---|---|
| Metric horsepower (PS) → Watt (W) | 735.49875 |
| Input | 1 Metric horsepower (PS) |
The first line is the headline result (horsepower (mechanical) → Watt (W)). Below it the power Converter lists input, which describe the same case from other angles. IEEE-754 double precision; displayed to the chosen number of decimal places (default 4). Very small or large results are shown in scientific notation.
Unit reference
Each unit expressed in the base unit used for the calculation. Conversions go through this base unit, so any unit can be converted to any other in the table.
| Unit | Equals (in watt) |
|---|---|
| Milliwatt (mW) | 0.001 |
| Watt (W) | 1 |
| Kilowatt (kW) | 1000 |
| Megawatt (MW) | 1000000 |
| Gigawatt (GW) | 1000000000 |
| Horsepower (mechanical) | 745.6998716 |
| Metric horsepower (PS) | 735.49875 |
| BTU per hour | 0.2930710702 |
| Microwatt (µW) | 0.000001 |
| Volt-ampere (VA, apparent power) | 1 |
| Kilovolt-ampere (kVA, apparent power) | 1000 |
Horsepower variants
Mechanical horsepower is 745.7 W, metric horsepower (PS) 735.5 W and electrical horsepower 746 W. A 150 hp engine is 111.9 kW mechanical.
Other units
1 BTU/h is 0.293 W, and 1 ton of refrigeration is 3.517 kW. Power is energy per unit time: 1 W is 1 J/s.
How the result changes with value
Holding every other input at the first worked example, this table changes only value. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Value | Horsepower (mechanical) → Watt (W) | Input |
|---|---|---|
| 0.5 | 372.8499 | 0.5 Horsepower (mechanical) |
| 1 | 745.6999 | 1 Horsepower (mechanical) |
| 2 | 1,491.3997 | 2 Horsepower (mechanical) |
| 4 | 2,982.7995 | 4 Horsepower (mechanical) |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Value: left empty shows "Enter value." beside that field and no result.
Choosing between the Power Converter and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Power of 2 Calculator](/math/power-of-2/) | exponent n | 2^10 |
| [Power Calculator](/science/power-calculator/) | use | Power |
| [Three-Phase Power Calculator](/engineering/three-phase-power-calculator/) | line-to-line voltage, line current and power factor | Real power |
| [Power Factor Calculator](/math/power-factor-calculator/) | real power and apparent power | Power factor |
| [Power-to-Weight Ratio Calculator](/engineering/power-to-weight-ratio/) | power, power unit and weight | Power-to-weight |
Background: unit conversion
Many customary units are defined exactly in terms of metric ones: since the 1959 International Yard and Pound Agreement an inch is exactly 2.54 cm and a pound is exactly 0.45359237 kg (NIST SP 811 lists these). So most length and mass conversions are exact apart from the rounding of the displayed result.
To convert, multiply the value by the source unit's factor to reach the base unit, then divide by the target unit's factor; the unit table on this page lists every factor used. Temperature and fuel economy are the exceptions, because they are not simple multiples.
Assumptions and limitations
- Negative values are allowed
- Zero converts to zero (except L/100 km, where zero is invalid)
- Units from different quantities cannot be converted
- Very large or tiny results switch to exponent notation
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for value to confirm this.
Frequently asked questions
How many watts is 1 kW?
1 kW is 1,000 watts; enter 1 kilowatt and choose watts as the target unit.
What is 100 kW in horsepower?
100 kW is about 134.1 mechanical horsepower (100 ÷ 0.7457).
What is a ton of cooling?
About 3.517 kW of heat removal.
What does the Power Converter calculate?
Convert watts, kilowatts, horsepower and BTU per hour. It returns Horsepower (mechanical) → Watt (W) and Input.
What formula does the Power Converter use?
result = value × (factor of source ÷ factor of target), base unit: watt. Every unit is defined by an exact or published factor to the base unit (watt).
What is an example of a power result?
With value 1, from Horsepower (mechanical), to Watt (W) and decimal places 4, the horsepower (mechanical) → Watt (W) is 745.6999.
Where does the method come from?
The method follows: NIST SP 811 (2008): mechanical horsepower = 745.69987158227022 W; Metric horsepower (PS) = 735.49875 W (DIN 66036).
Related calculators
- Power of 2 Calculator — Compute 2 raised to an integer power exactly.
- Power Calculator — Mechanical power from work and time, or force and velocity.
- Power Factor Calculator — Power factor, phase angle and reactive power from real and apparent power.
Sources
- NIST SP 811 (2008): mechanical horsepower = 745.69987158227022 W
- Metric horsepower (PS) = 735.49875 W (DIN 66036)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.