About the Power Converter
Power is the rate at which energy is used or produced — how much energy flows each second. It is measured in watts for light bulbs, appliances and power stations, in horsepower for car and boat engines, and in BTU per hour for heaters and air conditioners in the US. Car brochures from different countries may quote the same engine as 100 kW, 134 hp or 136 PS, which look like three different engines but are the same one.
This power converter converts between eight power units: watts, kilowatts, megawatts, mechanical horsepower, metric horsepower (PS), BTU per hour, kilocalories per hour and foot-pounds per second. It shows the result, the exact factor both ways, the power in every other unit, and the energy used in an hour at that power.
How to Use the Power Converter
Enter the power.
Choose the unit to convert from and to.
The result appears with the factor, all the other units, and the energy in kWh that one hour at this power would use.
How Power Conversion Works
Every unit is converted through the watt, one joule per second:
1 kW = 1,000 W 1 MW = 1,000,000 W
1 hp = 550 ft·lbf/s = 745.700 W (mechanical horsepower)
1 PS = 735.49875 W (metric horsepower)
1 BTU/h = 0.293071 W
1 kcal/h = 1.16222 W
result = value × (from-unit in W) ÷ (to-unit in W)
energy used (kWh) = power (kW) × hoursStep-by-Step Example
100 kW to horsepower.
To watts: 100 × 1,000 = 100,000 W
To horsepower: 100,000 ÷ 745.7 = 134.102 hp
To PS: 100,000 ÷ 735.49875 = 135.962 PSA 100 kW engine produces about 134.102 mechanical horsepower, or 135.962 PS.
One horsepower is 745.7 watts, about three-quarters of a kilowatt — roughly the cooking power of a small microwave oven.
Quick Reference
1 kW = 1.34102 hp = 1.35962 PS = 3,412.14 BTU/h
1 hp = 0.7457 kW = 1.01387 PS
1 PS = 0.735499 kW = 0.98632 hp
1,000 BTU/h = 0.293071 kWHorsepower and PS
James Watt defined horsepower in the 1780s to sell steam engines, from how much work a mill horse could do: 33,000 foot-pounds per minute, which is 550 per second. That became the mechanical horsepower of 745.7 watts. When European countries adopted metric units, they defined a slightly smaller metric horsepower, 75 kilogram-force metres per second, or 735.499 watts. It is called PS in Germany, CV in France, Italy and Spain, and pk in the Netherlands. The difference is about 1.4 percent, so an engine of 150 PS is about 148 hp. Today, official figures in the EU are in kilowatts, with PS often given alongside.
Power and Energy
Power is a rate; energy is an amount. A 2,000 watt kettle uses energy at 2 kilowatts, so running it for 3 minutes, 0.05 hours, uses 2 × 0.05 = 0.1 kWh. A 10 watt LED bulb left on for 100 hours uses 1 kWh. Electricity bills charge for energy, in kWh, so to estimate a running cost, multiply the power in kilowatts by the hours used and the price per kWh.
Heating and Cooling Equipment
Air conditioners and heaters in the US are rated in BTU per hour, often shortened to BTU. A 12,000 BTU/h unit, sometimes called one ton of cooling, moves about 3.517 kW of heat. That is the heat moved, not the electricity used: an efficient air conditioner or heat pump might move that heat using only about 1 kW of electricity.
Human and Machine Power
A person can produce about 100 watts of useful power for long periods, and a trained cyclist 250 to 400 watts for an hour. A family car's engine produces around 75 to 150 kW at full power, a large wind turbine a few megawatts, and a large power station more than 1,000 megawatts — a gigawatt.
Electrical Power
For electrical equipment, power is voltage multiplied by current: a 230 volt kettle drawing 10 amps uses 2,300 watts, and a 120 volt heater drawing 12.5 amps uses 1,500 watts. This is why the same appliance may be rated differently in different countries, and why circuits and fuses are sized by current. Large installations quote apparent power in volt-amperes, kVA, which equals kW only when the load is purely resistive; motors and some electronics draw a little more current than their real power suggests.
Power at Scale
Grid electricity is planned in megawatts and gigawatts. A typical home uses on average under half a kilowatt, though its peak demand while cooking or heating can reach several kilowatts. A large solar farm might produce 50 megawatts at midday, and a whole country's demand is measured in tens of gigawatts. Annual figures are then given in energy units, such as terawatt-hours, rather than power.
Understanding Your Result
The headline is the converted power.
The conversion factor shows the exact factor both ways.
The in every unit line gives the power in all eight units.
The also line shows the power in kW and hp, and the energy used by running at this power for one hour.
When Should You Use This Calculator?
Use it to compare engine outputs quoted in kW, hp or PS.
Use it for heating and air conditioning sizes in BTU per hour.
Use it to estimate electricity use from an appliance's wattage.
Use it for physics and engineering problems in watts.
Common Mistakes
Mixing hp and PS. Metric horsepower is about 1.4 percent smaller.
Confusing kW with kWh. One is power, the other energy.
Taking BTU/h as electricity use. For heat pumps and air conditioners it is heat moved, not power drawn.
Comparing peak and continuous power. Amplifiers and motors often quote a higher peak figure.
Forgetting efficiency. An engine's output is less than the fuel energy it burns.