Energy Converters
One calorie is 4.184 joules, one BTU is 1,055.06 joules, and one kilowatt-hour is 3.6 megajoules — three relationships that matter whether you're sizing a heating system, reading a nutrition label, or comparing electricity tariffs. A therm, used in gas billing, equals 100,000 BTU, which works out to just over 29.3 kilowatt-hours. Every tool on this page uses exact authoritative factors, so the answers you get from BTU to joule or therm to kilowatt-hour are consistent with NIST values, not rounded estimates.
The food "Calorie" printed on nutrition labels is actually a kilocalorie — 1,000 small calories, or 4,184 joules. That distinction trips up anyone converting between diet data and physics textbooks. The 20 converters here cover that gap alongside the other common scales: joules and kilojoules for science, BTU and therms for HVAC and gas, kilowatt-hours for electricity, and megajoules when the numbers get large. Each converter runs in both directions, so the reverse is one tap away.
Energy units evolved from separate fields — heat, mechanical work, electrical power — before the joule unified them in SI. That history left practical disciplines with their own preferred units: an HVAC engineer reaches for BTU, a utility bill quotes kWh, a chemist uses kilocalories, and a particle physicist works in electronvolts. Switching between those worlds is where a converter earns its keep. Start with the popular pairs below, or scroll for the full list.
Most popular
British Thermal Units to Therms
Convert british thermal units to therms and back.
BTU to Joules Converter
Convert British Thermal Units to joules and joules to BTU for heating and energy calculations.
Joules to Watt Seconds
Convert joules to watt seconds and back.
Kilocalories to Joules Converter
Convert kilocalories to joules — 1 kcal = 4,184 J. Food energy reference, calorie vs kilocalorie guide, and conversion table.
Joules to Megajoules Converter
Convert joules to megajoules and MJ to joules.
Megawatt Hours to Watt Hours
Convert megawatt hours to watt hours and back.
Therms to Kilowatt Hours
Convert therms to kilowatt hours and back.
Joules to Kilocalories Converter
Convert joules to kilocalories and kcal to joules.
All energy converters
Joules to Calories Converter
Convert joules to calories and calories to joules instantly with formula and common values.
Calories to Joules Converter
Convert calories to joules and joules to calories with precise conversion factor.
BTU to Joules Converter
Convert British Thermal Units to joules and joules to BTU for heating and energy calculations.
Joules to Kilowatt Hours Converter
Convert joules to kilowatt hours and kWh to joules.
Kilocalories to Calories Converter
Convert kilocalories to calories and calories to kilocalories.
Kilocalories to Joules Converter
Convert kilocalories to joules — 1 kcal = 4,184 J. Food energy reference, calorie vs kilocalorie guide, and conversion table.
Joules to Kilocalories Converter
Convert joules to kilocalories and kcal to joules.
Kilocalories to Kilojoules Converter
Convert kilocalories to kilojoules and kJ to kcal.
Electronvolts to Joules Converter
Convert electronvolts to joules and joules to eV.
Joules to Megajoules Converter
Convert joules to megajoules and MJ to joules.
British Thermal Units to Kilowatt Hours
Convert british thermal units to kilowatt hours and back.
British Thermal Units to Therms
Convert british thermal units to therms and back.
Calories to Megacalories
Convert calories to megacalories and back.
Joules to Watt Seconds
Convert joules to watt seconds and back.
Kilojoules to British Thermal Units
Convert kilojoules to british thermal units and back.
Megajoules to Calories
Convert megajoules to calories and back.
Megawatt Hours to Watt Hours
Convert megawatt hours to watt hours and back.
Million BTU to British Thermal Units
Convert million btu to british thermal units and back.
Therms to Kilowatt Hours
Convert therms to kilowatt hours and back.
Watt Seconds to Joules
Convert watt seconds to joules and back.