Energy & Power Converters
Convert between joules, kilowatt-hours, calories, BTU, watts, and horsepower. Plus calculate your electricity costs.
Energy Conversions
Joules to Calories
1 cal = 4.184 J (exact by definition)
Calories to Joules
1 cal = 4.184 J (exact)
Kilowatt-hours to Joules
1 kWh = 3,600,000 J (exact: 1000 W × 3600 s)
Joules to Kilowatt-hours
1 kWh = 3,600,000 J (exact)
Kilowatt-hours to Megajoules
1 kWh = 3.6 MJ (exact)
Megajoules to Kilowatt-hours
1 MJ = 1/3.6 kWh ≈ 0.27778 kWh
BTU to Kilowatt-hours
1 BTU (IT) = 1055.05585262 J
Kilowatt-hours to BTU
1 kWh = 3,600,000 J
Power Conversions
Frequently Asked Questions
What is the difference between energy and power?
Energy is the total work done (measured in joules or kWh). Power is the rate of doing work (measured in watts). Energy = Power × Time.
What is a kilowatt-hour (kWh)?
The energy consumed by a 1 kW device running for 1 hour. It equals 3,600,000 joules. Used for electricity billing.
What is the difference between a calorie and a Calorie?
A calorie (cal) is a small unit. A food Calorie (Cal or kcal) = 1000 cal = 4184 J.
How is horsepower defined?
1 mechanical hp ≈ 745.7 watts. Originally defined by James Watt to compare steam engines to horses.
What is a BTU?
British Thermal Unit — the energy to raise 1 pound of water by 1°F. About 1055 joules. Common in US HVAC.
How do I calculate electricity cost?
Cost = kWh × tariff. kWh = (watts ÷ 1000) × hours. Use our electricity cost calculator for quick estimates.