Unit Conversion
Energy Converter: Joules, kWh, BTU, Calories
Convert 13 energy units instantly, compare every result and calculate energy from power and time.
Convert energy
Calculation
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Energy from power and time
Calculation
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kW is power; kWh is energy. The power × time estimate does not include real-world losses.
All equivalent values
Electricity and SI
Heat
Food energy
Physics
Energy scale
Bars use a logarithmic scale; equal visual steps do not mean equal energy differences.
Unit notes
1 small cal = 4.184 J. 1 kcal = 1,000 cal = 1 dietary Calorie (Cal).
BTU uses the International Table definition. US therm is approximate and differs from EC therm.
1 kWh = 3,600,000 J = 3.6 MJ
1 eV = 1.602176634 × 10⁻¹⁹ J
Height changes gravitational potential energy
Worked example: watts and hours to kWh and joules
A device drawing a constant 1,500 W for 2 hours uses 1.5 kW × 2 h = 3 kWh. Because 1 kWh = 3,600,000 J, this is 10,800,000 J or 10.8 MJ. Enter the power and duration in the panel above, then choose the energy unit you need.
Watts describe power; watt-hours describe energy accumulated over time. A device that cycles on and off will use a different amount from a constant-power estimate.
Use the power converter when your starting specification is in hp, W or kW. To estimate the bill using your own price per kWh, use the electricity cost calculator.
Energy Converter FAQ
How many joules are in one kWh?
One kilowatt-hour equals 3,600,000 joules.
How do I convert joules to kWh?
Divide joules by 3,600,000.
How many joules are in one BTU?
One international table BTU is about 1,055.06 joules.
How many joules are in one calorie?
One small calorie is about 4.184 joules.
Is energy the same as power?
No. Energy is an amount of work or heat. Power is the rate of using or transferring energy.
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