Free online energy converter. Convert joules, kilowatt-hours (kWh), calories, BTU, therms, and watt-hours instantly — for electricity bills, food energy, HVAC, and physics. Accurate, instant, no sign-up.
Joule • kWh • calorie • BTU • therm
US utilities bill per kWh (avg ~16¢/kWh in 2026). Convert appliance joules or watt-hours to kWh to estimate running costs.
Nutrition labels list food Calories (kcal). Convert to joules (the SI unit used outside the US) when reading international labels.
Furnaces and AC are rated in BTU. Natural gas bills use therms. Convert to kWh to compare energy sources fairly.
Energy comes in many units depending on context, and the joule (J) is the SI base unit that ties them all together. For US households, the most useful conversion is to kilowatt-hours (kWh): 1 kWh = 3,600,000 joules = 3.6 megajoules. Your electricity bill is measured in kWh, and at the 2026 US average of about 16 cents per kWh, knowing how to convert appliance energy ratings helps estimate running costs. A 1,500-watt space heater run for one hour uses 1.5 kWh = 5.4 million joules ≈ 24 cents.
For food, the "Calorie" on nutrition labels is actually a kilocalorie (kcal) = 4,184 joules. A 2,000-Calorie daily diet equals 8.37 million joules of energy. In heating and cooling, the British Thermal Unit (BTU) dominates US specs: 1 BTU = 1,055 joules, and 1 kWh = 3,412 BTU. Natural gas is billed in therms, where 1 therm = 100,000 BTU = 29.3 kWh = 105.5 million joules. Understanding these relationships lets you compare the true cost and efficiency of electricity, gas, and other energy sources on equal footing.
LED bulb (10W, 1hr): 0.01 kWh. Laptop (50W, 8hr): 0.4 kWh. Refrigerator: ~1.5 kWh/day. Central AC: 3 kWh/hr. EV charge (full): 50–100 kWh.
1 gallon gasoline: ~33.7 kWh (121 MJ). 1 cubic foot natural gas: ~0.3 kWh. AA battery: ~0.004 kWh. Tesla Model 3 battery: ~60 kWh.
Apple: 95 kcal = 397 kJ. Slice of pizza: 285 kcal. Big Mac: 563 kcal = 2,356 kJ. Daily diet: 2,000 kcal = 8.4 MJ. 1 lb of fat ≈ 3,500 kcal.
1 BTU = 1,055 J. Window AC: 5,000–12,000 BTU/hr. Furnace: 40,000–100,000 BTU/hr. 1 therm natural gas = 29.3 kWh.
Energy units proliferated because each industry measured a different thing: the joule from mechanics, the calorie from heat, the BTU from heating fuel, the kilowatt-hour from electricity billing and the therm from gas supply. All express the same physical quantity, so all convert exactly. Two traps recur. The food "Calorie" with a capital C is a kilocalorie — 1,000 small calories — so a 2,000-Calorie diet is 2 million calories in physics terms. And the kilowatt-hour is energy while the kilowatt is power; confusing them is the single most common error on an electricity bill.
joules = value × factor_fromresult = joules ÷ factor_to1 kWh = 3.6 MJ · 1 BTU = 1055.06 J · 1 cal = 4.184 J · 1 kcal = 4,184 Jwhere:
Assumptions: The thermochemical calorie (4.184 J) is used here. The International Table calorie is 4.1868 J, a 0.03% difference that matters only in precise thermodynamic work.
A typical US household month expressed in the units other industries would use.
Result850 kWh = 3,060 MJ = 2.90 million BTU = 29.0 therms
The therm figure is the useful one when comparing heating options: if gas costs $1.20 a therm and electricity $0.16 a kWh, the same delivered energy costs $34.80 by gas against $136 by resistive electric heat — before accounting for appliance efficiency.