Power Unit Converter
Convert power values between watts, kilowatts, megawatts, milliwatts, horsepower (hp and PS), BTU per hour, foot-pounds per second, and kilocalories per hour. Enter a value, pick the units, and get an instant result.
Convert Power Units
Power Units Formula
Where:
- \(P_{\text{source}}\) — the power value you enter, in the source unit
- \(f_{\text{source}}\) — conversion factor of the source unit to watts (W)
- \(f_{\text{target}}\) — conversion factor of the target unit to watts (W)
- \(P_{\text{target}}\) — the converted power value, in the target unit
The calculator first converts the entered value into the base unit (the watt) and then divides by the factor of the target unit. This two-step method lets any of the ten supported units be converted into any other with a single multiplication and division.
Power Units – Calculation Example
Example: convert 1000 W (the power of a small electric heater) into mechanical horsepower.
\[ f_{\text{W}} = 1, \quad f_{\text{hp}} = 745.699872 \]
\[ P_{\text{hp}} = 1000 \times \frac{1}{745.699872} = 1.341022089 \]
Result: 1000 W ≈ 1.341022089 hp. In other words, a 1 kW device delivers about 1.34 mechanical horsepower.
How to use the calculator
- Enter the power value you want to convert in the Power value field (the default is 1000).
- Choose the unit you are converting from in the From unit dropdown — watts, kilowatts, megawatts, milliwatts, mechanical horsepower, metric horsepower (PS), BTU/h, BTU/min, ft·lbf/s, or kcal/h.
- Choose the unit you want to convert to in the To unit dropdown.
- Read the result in the Converted Power field. The value updates automatically whenever you change an input.
What is power and why convert its units?
Power is the rate at which energy is transferred or work is done. The SI unit is the watt (W), defined as one joule of energy per second. Because practical applications span an enormous range — from microwatts in sensors to gigawatts in power plants — many multiples and alternative units have evolved, and converting between them is a daily task in engineering, HVAC, automotive work, and energy billing.
Different industries favor different units. Electrical and heating engineers work in watts and kilowatts; American HVAC specifications are often quoted in BTU per hour; car engines are rated in horsepower (hp) in the US and UK, or metric horsepower (PS, from the German Pferdestärke) in Europe; and heating systems in some countries are sized in kilocalories per hour. When a specification sheet uses one unit and your calculation needs another, this converter closes the gap instantly and without arithmetic errors.
Note that the two horsepower units are not the same: 1 mechanical (imperial) horsepower equals 745.699872 W, while 1 metric horsepower (PS) equals only 735.49875 W — a difference of about 1.4%. A 150 PS European engine therefore produces about 147.6 hp, not 150 hp. Confusing the two is one of the most common mistakes in power conversion.
Conversion factors used
All units are converted through the watt, using these exact factors:
| Unit | Symbol | Value in watts (W) |
|---|---|---|
| Watt | W | 1 |
| Kilowatt | kW | 1 000 |
| Megawatt | MW | 1 000 000 |
| Milliwatt | mW | 0.001 |
| Mechanical horsepower | hp | 745.699872 |
| Metric horsepower | PS | 735.49875 |
| BTU per hour (IT) | BTU/h | 0.29307107 |
| BTU per minute (IT) | BTU/min | 17.5842642 |
| Foot-pound-force per second | ft·lbf/s | 1.355817948 |
| Kilocalorie per hour | kcal/h | 1.163 |
Assumptions, limitations and tips
- BTU convention: the calculator uses the International Table (IT) British thermal unit. Older US tables may differ by roughly 0.06%, which matters only at very high precision.
- Horsepower type: only mechanical (imperial) horsepower and metric horsepower (PS) are supported. Boiler horsepower (≈ 9 810 W) and electrical horsepower (746 W exactly) are intentionally excluded.
- Instantaneous vs. per-hour units: watts, hp and ft·lbf/s describe instantaneous power, while BTU/h and kcal/h describe energy per hour. They are still all rates of energy transfer and convert directly into one another.
- Negative values are rejected, since the tool is designed for magnitude conversions. If you need to indicate power flow direction, keep the sign separately.
- Quick sanity checks: 1 kW ≈ 1.341 hp ≈ 1.36 PS ≈ 3 412 BTU/h; 1 MW = 1 000 kW; 1 hp ≈ 2 545 BTU/h.
Power often appears together with rotation and heat. If your project also involves rotating machinery, try our Torque Converter or the Angular Velocity Converter; for thermal applications, the Thermal Conductivity Converter and the Viscosity Converter cover the remaining unit conversions you may need.
Frequently Asked Questions
How do I convert watts to horsepower by hand?
Divide the watt value by 745.7 to get mechanical horsepower: \( P_{\text{hp}} = P_{\text{W}} / 745.699872 \). For metric horsepower (PS), divide by 735.5 instead. For example, a 2200 W motor gives \( 2200 / 745.7 \approx 2.95 \) hp. Going the other way, multiply horsepower by the same factor to get watts. Keep at least four significant digits of the factor if you need results accurate to about 0.01%.
What is a good power output for household appliances?
Typical values help you sanity-check conversions: an LED bulb uses 5–15 W, a laptop charger 45–100 W, a microwave 700–1200 W, an electric kettle 2000–3000 W, and a home air conditioner 2000–5000 W (roughly 7000–17000 BTU/h). A residential solar installation is often rated 3–10 kW. If your converted value falls far outside these ranges, you have probably picked the wrong unit or misplaced a decimal.
How many BTU per hour is 1 kW?
One kilowatt equals approximately 3412 BTU/h. This is the key conversion for HVAC work: an air conditioner rated at 12,000 BTU/h draws about \( 12000 \times 0.29307107 \approx 3517 \) W, or roughly 3.5 kW of heating/cooling capacity. Note that BTU/h describes heat flow rate, so it converts directly to watts — no time division is needed.
Why are hp and PS different, and which should I use?
Mechanical (imperial) horsepower is 745.7 W, while metric horsepower (PS) is 735.5 W — about 1.4% less. Use hp for US and UK vehicle specs, and PS (Pferdestärke) for European ones. A 150 PS engine is only about 147.6 hp, so mixing them up inflates or shrinks ratings. Some markets also quote kW directly (EU type approval does), so a 100 kW engine equals about 136 PS or 134 hp.
Can I use this converter for cooling capacity and heating systems?
Yes. Cooling and heating capacities are power values, just expressed in BTU/h (common in North America) or kcal/h (common in some European and Asian countries). Convert them to watts or kilowatts to compare equipment or estimate energy costs. One kcal/h equals 1.163 W, and 1000 kcal/h ≈ 1.163 kW. For running costs, remember that capacity in kW multiplied by operating hours gives energy in kWh, which your electricity bill uses.
What is the difference between BTU and BTU per hour?
BTU is a unit of energy (about 1055 joules), while BTU per hour is a unit of power — the rate at which that energy is transferred. Appliance ratings always mean BTU/h, even when the label is shortened to just "BTU". This converter handles only power units, so enter BTU/h or BTU/min values. If you have a plain energy figure in BTU, you first need a time period before any power conversion makes sense.
How do I convert power to energy or electricity cost?
Power alone doesn't give cost — you need time. Multiply power in kW by hours of use to get energy in kWh, then multiply by your electricity rate. A 1500 W heater running 5 hours uses \( 1.5 \times 5 = 7.5 \) kWh. Rates vary by region and tariff, so check your utility bill for the exact price per kWh before estimating expenses.