Energy Converter
Convert between Joules, watt-hours, kilowatt-hours, and BTU. Pick a unit on the left and one on the right, enter a value, and copy the result.
Convert between Joules (J), watt-hours (Wh), kilowatt-hours (kWh), and BTU. Select the From unit in the left table and the To unit in the right table, enter a value, and copy the result. Decimal places can be set from 0 to 10.
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Examples
- 1 Wh → 3600 J
- 1 kWh → 3.6 MJ
- 1 BTU → 1055 J
FAQ
How many Joules in a watt-hour?
1 Wh = 3600 J (1 watt × 1 hour = 3600 seconds).
How many Joules in a kilowatt-hour?
1 kWh = 3,600,000 J (3.6 million joules).
What is BTU?
BTU (British Thermal Unit) is a unit of energy. 1 BTU ≈ 1055 J. BTUs are used in the US for heating and cooling systems (e.g. air conditioner capacity).
What is the difference between power and energy?
Power is the rate of energy use (watts = joules per second). Energy is the total amount consumed over time (watt-hours = watts × hours). A 100 W bulb used for 10 hours consumes 1 kWh of energy.
How do I read my electricity bill in kWh?
Your electricity meter measures consumption in kilowatt-hours (kWh). If you use a 2000 W heater for 5 hours, that is 2 kW × 5 h = 10 kWh. Multiply by your rate (e.g. $0.15/kWh) to get the cost: $1.50.
What is a food calorie (kcal)?
A food calorie is actually a kilocalorie (kcal) = 4184 joules. A 100-calorie snack provides 418,400 J of chemical energy. The small calorie (cal) = 4.184 J is used in chemistry.
How many BTUs does an air conditioner need for a room?
A rule of thumb: multiply the room area in square feet by 20 to get the BTU requirement. A 300 sq ft room needs roughly 6,000 BTU/hour. Most window AC units are rated in BTU/hr.
How many joules are in a car battery?
A typical 12V 60Ah car battery stores 12 × 60 = 720 Wh = 2,592,000 J (about 2.6 MJ). An EV battery is much larger: a 75 kWh pack stores 270,000,000 J.
What is a megajoule (MJ) used for?
MJ is used for large-scale energy: household appliances (a microwave uses ~0.5 MJ per hour), fuel energy content (1 liter of gasoline ≈ 34 MJ), and industrial energy measurement.
How do calories and kilojoules compare on food labels?
Food energy is shown in kcal (calories) in the US and kJ in many other countries. 1 kcal = 4.184 kJ. A 2000 kcal daily diet equals about 8,368 kJ.
What is the energy content of common fuels?
1 liter of gasoline ≈ 34 MJ. 1 liter of diesel ≈ 37 MJ. 1 kg of coal ≈ 24 MJ. 1 cubic meter of natural gas ≈ 38 MJ. 1 kWh of electricity ≈ 3.6 MJ (but producing it from fuel is less efficient).