Converter Tools
Energy Converter
Convert energy between joules, kilojoules, calories, kcal, watt-hours, kWh, BTU, therms, ft-lb, and electronvolts in your browser.
Quick conversions
From unit
SI / metric
J, kJ, MJ, GJ, mJ, erg
Thermal / nutrition
cal, kcal, cal_IT, BTU, therm
Electrical
Wh, kWh, MWh
Mechanical / imperial
ft-lb, in-lb, hp-hr
Atomic
eV, keV, MeV
Fuel and references
ton TNT, boe
Decimal places
Show units
SI / metric results
The joule is the SI base unit of energy. 1 kJ is 1000 J. 1 MJ is 1000 kJ. 1 erg equals 10^-7 J.
Converted
Joule
1000000 J
SI base unit. One newton-meter, or one watt-second. Default in physics and engineering.
Source
Kilojoule
1000 kJ
Used on European nutrition labels and small mechanical work. 1 kJ equals 1000 J.
Converted
Megajoule
1 MJ
Larger lab and industrial scale. 1 MJ is 1000 kJ. Typical car fuel tank holds 1500 to 2500 MJ.
Converted
Gigajoule
0.001 GJ
Heating bills in some markets. 1 GJ equals 1000 MJ, roughly 278 kWh.
Converted
Millijoule
1000000000 mJ
Small impulses such as laser pulses, sensors, and capacitor discharges.
Converted
Erg
10000000000000 erg
CGS unit. 1 erg equals 10^-7 J. Common in older physics and astrophysics papers.
Thermal and nutrition results
1 cal equals 4.184 J (thermochemical). 1 kcal equals 1 food Calorie equals 4184 J. 1 BTU equals 1055.056 J.
Converted
Calorie (thermochemical)
239005.7361 cal
Small calorie. 1 cal heats 1 g of water by ~1 deg C. Defined as exactly 4.184 J.
Converted
Kilocalorie (food Calorie)
239.0057 kcal
Food energy on labels. 1 kcal equals 1 Cal (big C) equals 1000 cal equals 4184 J.
Converted
Calorie (IT)
238845.8966 cal_IT
International Table calorie used in steam and HVAC tables. Defined as exactly 4.1868 J.
Converted
British thermal unit (IT)
947.8171 BTU
US heating and cooling. 1 BTU raises 1 lb of water by 1 deg F. Air conditioners are rated in BTU/h.
Converted
Therm (US)
0.0095 therm
Natural gas billing unit. 1 US therm equals 100,000 BTU equals about 29.3 kWh.
Electrical results
1 Wh equals exactly 3600 J. 1 kWh equals 3.6 MJ. Utility bills are usually in kWh.
Converted
Watt-hour
277.7778 Wh
Battery capacity for phones, laptops, and small UPS units. 1 Wh equals 3600 J exactly.
Converted
Kilowatt-hour
0.2778 kWh
Electric utility billing unit. 1 kWh equals 3.6 MJ. A typical home uses 10 to 30 kWh per day.
Converted
Megawatt-hour
0.0003 MWh
Grid and industrial energy. 1 MWh equals 1000 kWh equals 3.6 GJ.
Mechanical / imperial results
1 ft-lb equals 1.3558 J. 1 ft-lb equals 12 in-lb. 1 hp-hr equals about 2.685 MJ.
Converted
Foot-pound force
737562.1493 ft-lb
US torque and work. 1 ft-lb equals 1.355818 J. Common in automotive specs.
Converted
Inch-pound force
8850745.7913 in-lb
Smaller mechanical work and torque. 1 ft-lb equals 12 in-lb exactly.
Converted
Horsepower-hour
0.3725 hp-hr
Mechanical horsepower running for one hour. 1 hp-hr equals about 2.685 MJ.
Common conversions, in plain English
- 1 kWh equals exactly 3.6 megajoules (MJ).
- 1 food Calorie (Cal) equals 1 kcal equals 4184 joules.
- 1 kcal equals 4.184 kJ exactly, so dividing kJ by 4.184 gives kcal.
- 1 BTU equals 1055.05585 J. A 12,000 BTU/h air conditioner moves about 3.5 kW of heat.
- 1 US therm equals 100,000 BTU equals about 29.3 kWh of heating energy.
- 1 eV equals 1.602176634e-19 J since the 2019 SI redefinition.
- 1 ton of TNT is defined as exactly 4.184 gigajoules (1e9 cal).
- 1 horsepower-hour equals about 2.685 MJ, or roughly 0.7457 kWh.
Common reference energies
Tap any reference to load its joule value. Every unit updates instantly.
How to use
- Pick a quick conversion preset, or type a number into the energy value field.
- Select the source unit (J, kJ, kWh, kcal, BTU, ft-lb, eV, and more) from the From unit picker.
- Every other supported unit recomputes instantly. The source card is highlighted, and every converted card has a Copy button.
- Adjust Decimal places for short or scientific output, and use Show units to hide atomic-scale units when you do not need them.
- Tap any reference energy at the bottom (AA battery, kWh per home per day, gallon of gasoline, ton of TNT) to load that value and compare it across every unit.
About this tool
Energy Converter changes a value between every common unit of energy and work in one view. Type a number, pick the source unit, and every other supported unit updates instantly. Coverage spans SI / metric units (joule, kilojoule, megajoule, gigajoule, millijoule, erg), thermal and nutrition units (small calorie, kilocalorie / food Calorie, International Table calorie, BTU, US therm), electrical units (watt-hour, kilowatt-hour, megawatt-hour), mechanical / imperial units (foot-pound force, inch-pound force, horsepower-hour), atomic-scale units (electronvolt, keV, MeV), and large reference scales (ton of TNT, barrel of oil equivalent). Every factor is exact or based on the standard NIST and CODATA conventional value: 1 calorie equals exactly 4.184 J (thermochemical), 1 BTU equals exactly 1055.05585262 J (International Table), 1 kWh equals exactly 3,600,000 J, 1 eV equals exactly 1.602176634 x 10^-19 J (since the 2019 SI redefinition), and 1 ton of TNT equals exactly 4.184 GJ. Helpful behaviors include free-form input parsing ("100 kcal", "1.5 kWh", "2,5 MJ"), an auto-suggested unit swap when the text suffix does not match the selected From unit, a Decimal places control for short or scientific output, a Show units filter (All, Everyday, Scientific) to hide units you do not need, quick-conversion presets for the most-searched pairs (kJ to kcal, kWh to BTU, eV to J, ft-lb to J), and a Common reference energies panel with real-world examples (AA battery, smartphone battery, EV battery, US household daily kWh, gallon of gasoline, marathon runner energy use, lightning bolt, Hiroshima bomb yield). Useful for converting European kJ labels to US kcal, reading utility bills in different units, sizing battery capacity against electrical loads, checking BTU air conditioner ratings against kWh, converting physics homework between joules and electronvolts, or running back-of-the-envelope estimates for fuel and explosives. All math runs locally in your browser. Numbers never leave your device.
Free to use. Works in your browser. No signup, no login.
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