Power Converter
Convert watts, microwatts, milliwatts, kilowatts, megawatts, mechanical horsepower, BTU per hour, and kilocalories per hour. Enter a number in either field for an instant result.
Convert Power Instantly
Choose units, edit either number, or tap a popular conversion.
1 W equals 0.001 kW
Popular power conversions
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How to Use the Power Converter
Use this calculator when you already know a power value and want it expressed in another power unit. It converts electrical, mechanical and heating power units using fixed definitions.
Enter power
Type a non-negative number in either measurement field.
Select units
Pick watts, horsepower, BTU per hour or another supported unit.
Read your result
Review the updated conversion factor and chart, then copy the answer.
Power Conversion Formula
Power measures how quickly energy is transferred or work is done. The watt (W) is the SI unit of power: 1 W = 1 joule per second. Each dropdown option has a known watt equivalent, so conversions use this common reference.
General formula
Converted value = Input × (watts per source unit ÷ watts per destination unit)Example: 2.5 kilowatts to watts
2.5 × 1,000 = 2,500 watts.
Example: 1 mechanical horsepower to kilowatts
745.699871582 W ÷ 1,000 ≈ 0.745699871582 kW.
Example for your current unit selection: 5 W × 0.001 = 0.005 kW.
Power vs. energy: Watts and kilowatts are power. Watt-hours, kilowatt-hours, BTU without “per hour,” and kilocalories without “per hour” are energy. Converting power to energy requires an elapsed time.
Power Conversion Table
This table updates automatically with your selected units. Intermediate calculations use the specified factors without rounding; the display may round long decimals.
| Watts (W) | Kilowatts (kW) |
|---|---|
| 1 | 0.001 |
| 2 | 0.002 |
| 5 | 0.005 |
| 10 | 0.01 |
| 25 | 0.025 |
| 50 | 0.05 |
| 100 | 0.1 |
| 1000 | 1 |
Common values: 1, 2, 5, 10, 25, 50, 100, and 1,000 source units.
Power Units and Conversion Factors
The eight units below represent rates of energy transfer. Mechanical horsepower and thermal energy conventions are clearly identified to avoid mixing unit definitions.
| Power unit | Equivalent in watts | Typical use |
|---|---|---|
| 1 microwatt (µW) | 0.000001 W | Small electrical signals |
| 1 milliwatt (mW) | 0.001 W | Low-power devices |
| 1 watt (W) | 1 W | SI power unit |
| 1 kilowatt (kW) | 1,000 W | Electrical equipment |
| 1 megawatt (MW) | 1,000,000 W | Large-scale power |
| 1 mechanical horsepower (hp) | 745.699871582 W | Mechanical engines |
| 1 BTU per hour (IT) | 0.293071070172 W | Heating and cooling ratings |
| 1 kilocalorie per hour (th) | 1.16222222222 W | Thermal power rates |
What is the difference between watts and horsepower?
Watts are the standard SI unit of power. Horsepower is a traditional power rating used for engines and motors. This calculator uses mechanical horsepower (about 745.7 watts per hp). Metric horsepower, also called PS, has a different value and is not represented by this dropdown.
BTU per hour and kilocalories per hour
BTU/h and kcal/h measure thermal power, such as the rate of heating or cooling. This tool uses the International Table BTU (approximately 1,055.05585262 joules per BTU) and the thermochemical kilocalorie (exactly 4,184 joules per kcal). The names refer to rates because the energy units are divided by one hour.
Microwatts, milliwatts and megawatts
One watt equals 1,000 milliwatts or 1,000,000 microwatts. One megawatt equals 1,000 kilowatts or 1,000,000 watts. Smaller units are useful for low-power signals; larger units are useful for generators and industrial equipment.
Frequently Asked Questions
What is the difference between watts and kilowatts?
One kilowatt is exactly 1,000 watts. Divide watts by 1,000 to get kW, or multiply kilowatts by 1,000 to get watts.
How many watts are in one mechanical horsepower?
One mechanical horsepower is approximately 745.699871582 watts. This tool uses mechanical horsepower, not metric horsepower (PS).
How do I convert BTU per hour to watts?
Multiply BTU per hour by approximately 0.293071070172 to get watts. The converter uses the International Table BTU definition.
What is a kilocalorie per hour?
A kilocalorie per hour is a rate of energy transfer, so it measures power. We use the thermochemical kilocalorie: 1 kcal = 4,184 joules; hence 1 kcal/h = 1.16222222222 watts.
Are BTU and BTU per hour the same?
No. BTU is an energy amount, whereas BTU per hour is power, an energy-transfer rate. This tool converts BTU per hour.
Can this tool convert watts to kilowatt-hours?
No. Kilowatt-hours measure energy. Converting power to energy requires an elapsed time. Use a power-to-energy calculator for that.
How do I convert watts to amps?
Watts and amps measure different electrical quantities. Converting between them requires the voltage, and AC systems may also need power factor.
Does one horsepower always equal the same number of watts?
Different horsepower conventions exist. This converter uses mechanical horsepower, approximately 745.699871582 W per hp.
Why are kilocalories per hour different from food Calories?
A food Calorie is a kilocalorie of energy. Dividing by hours expresses a rate; a food Calorie alone does not measure power.
Can I enter fractional or scientific-notation amounts?
Yes. Enter values such as 0.25, 2.5, 1e-6 or 1.2e9. Very large and small results may display in scientific notation.
Are negative power measurements supported?
This unit-conversion tool is intended for non-negative power magnitudes. Signed power flow or power export can be modeled separately.
Will the calculator work without signing in?
Yes. The conversion runs directly in the browser and does not need an account or a server calculation.
Related Calculators
If you need to calculate electrical current, apparent power or energy usage, those calculations require extra information and belong in separate tools.
Conversion References
Unit factors are drawn from the NIST Guide to the SI, Appendix B.9 and Appendix B.8. Reference definitions are specified because BTU and horsepower can refer to more than one convention.