Convert Kilowatt-hours (kWh) to Joules (J)

Energy is the amount of work that can be done, measured in joules or kilowatt-hours. Power is the rate at which energy is used or transferred, measured in watts. Think of energy as the total amount of fuel in a tank, and power as how fast you're using that fuel. 1 kilowatt of power used for 1 hour equals 1 kilowatt-hour of energy.

1 calorie (cal) = 4.184 joules (J). To convert calories to joules, multiply by 4.184. To convert joules to calories, divide by 4.184. Note that food 'calories' are actually kilocalories (kcal), so 1 food calorie = 4,184 joules. This is why a 100-calorie snack contains 418,400 joules of energy.

1 kilowatt-hour (kWh) = 3,600,000 joules (3.6 MJ). This comes from: 1 kW = 1,000 watts, 1 hour = 3,600 seconds, so 1 kWh = 1,000 × 3,600 = 3,600,000 joule-seconds = 3.6 megajoules. Your electric bill measures energy in kWh because it's more practical than using millions of joules.

1 BTU (British Thermal Unit) = 1,055.06 joules ≈ 0.293 watt-hours. BTUs are commonly used in HVAC systems. For reference: a typical home air conditioner might be rated at 12,000 BTU/hour (3.5 kW), and a gallon of gasoline contains about 114,000 BTU (33.4 kWh) of energy.

Electron volts measure very small amounts of energy at the atomic and subatomic level. 1 eV = 1.602 × 10⁻¹⁹ joules. Common units are keV (1,000 eV), MeV (1,000,000 eV), and GeV (1,000,000,000 eV). X-rays have energies of 1-100 keV, while particle accelerators can produce beams with GeV energies.

The average US home uses about 10,500 kWh per year (37.8 GJ), or roughly 29 kWh per day. This varies greatly by region, home size, and efficiency. For comparison, this is equivalent to about 9 billion calories, 36 million BTU, or enough energy to lift a car 2,400 miles straight up against gravity.

Mechanical energy units like foot-pounds (ft⋅lb) measure work done by forces - like lifting weights or tightening bolts. Thermal energy units like calories and BTUs measure heat energy. While both can be converted to joules, they represent different types of energy transfer. 1 ft⋅lb = 1.356 J, while 1 cal = 4.184 J.