Energy & Power Converter

Convert between energy units (joule, kWh, BTU, calorie, therm, ft·lb, electronvolt) and power units (watt, kilowatt, horsepower, BTU/h) in one tool.

Energy value

All energy units

Click any result to copy the value.

Quick reference

Energy conversion table (1 unit = …)
FromEquivalent
1 kWh3 600 000 J = 3.6 MJ = 3412.14 BTU = 859.845 kcal
1 MJ1 000 000 J = 0.2778 kWh = 947.82 BTU = 238.85 kcal
1 BTU1055.06 J = 0.000293 kWh = 0.252 kcal
1 kcal4184 J = 3.9657 BTU = 0.001163 kWh
1 therm (US)105 480 400 J = 29.3 kWh = 100 000 BTU
1 ft·lb1.3558 J = 0.3238 cal
Power conversion table (1 unit = …)
FromEquivalent
1 kW1000 W = 1.341 hp (mech) = 1.360 PS = 3412.14 BTU/h
1 hp (mech)745.70 W = 0.7457 kW = 1.0139 PS = 2544.43 BTU/h
1 PS (metric hp)735.50 W = 0.7355 kW = 0.9863 hp (mech)
1 BTU/h0.29307 W = 0.0002931 kW
1 MW1 000 000 W = 1341.02 hp (mech)
1 ft·lb/s1.3558 W = 0.001818 hp (mech)

FAQ

What is the difference between metric and mechanical horsepower?
Mechanical (imperial) horsepower is defined as 550 ft·lb/s which equals 745.6999 W. Metric horsepower (PS, cheval-vapeur) is defined as 75 kgf·m/s which equals 735.49875 W. Metric horsepower is roughly 1.4% smaller than mechanical horsepower. Car engines in Europe are usually rated in PS, while US specifications typically use mechanical hp.
What is a BTU?
A British thermal unit (BTU) is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. The ISO-standard BTU equals 1055.06 joules. BTU is widely used in HVAC — air conditioner and heater capacities are commonly given in BTU per hour (BTU/h).
Why is a food calorie actually a kilocalorie?
In nutrition, "Calorie" (capitalised) or "kcal" equals 1000 small calories. A small calorie (cal, 4.184 J) raises 1 g of water by 1°C. A food Calorie (kcal, 4184 J) raises 1 kg of water by 1°C. So a 2000 Cal daily diet is actually 2 000 000 cal or about 8.368 MJ.
How do I convert kWh to joules?
Multiply by 3 600 000. One kilowatt-hour is the energy produced by 1000 watts of power running for 3600 seconds, which equals 3.6 megajoules. For example, 5 kWh = 18 000 000 J = 18 MJ.
What is a therm and when is it used?
A therm is a unit of heat energy equal to 100 000 BTU, or about 105.48 MJ (29.3 kWh). It is commonly used to bill natural gas in the United States and United Kingdom. One therm is roughly the energy released by burning 100 cubic feet of natural gas.
Is 1 kW the same as 1 kWh?
No. Kilowatt (kW) is a unit of power — the rate at which energy is used or produced. Kilowatt-hour (kWh) is a unit of energy — power multiplied by time. A 2 kW heater running for 3 hours consumes 2 × 3 = 6 kWh of energy. To convert power to energy you must specify a time interval.

This converter handles two related domains in a single tabbed interface. The Energy tab converts between joule, kilojoule, megajoule, gigajoule, kilowatt-hour, megawatt-hour, small calorie, kilocalorie (food Calorie), BTU, therm, foot-pound and electronvolt. Type a value, pick the source unit, and every other unit updates instantly — click any result to copy it to the clipboard. For example, entering 1 kWh shows 3 600 000 J, 3412.14 BTU, 859.85 kcal and 3.6 MJ side by side. The Power tab covers watt, kilowatt, megawatt, gigawatt, metric horsepower (PS = 735.499 W), mechanical horsepower (745.700 W), BTU per hour, calorie per second and foot-pound per second. Entering 200 PS reveals 147.10 kW and 197.26 mechanical hp. Preset chips jump to common values (1 kWh, 100 kcal, 24 kW boiler, 200 PS engine, 12 000 BTU/h).