Energy & Work Converter
Convert between units of energy — joules, kilojoules, megajoules, watt-hours, kilowatt-hours, calories, kilocalories, BTU, foot-pounds, newton-metres and MeV. Pick any two units; it runs entirely in your browser, with exact conversion factors.
Energy conversions come up everywhere — turning an appliance rating from kilojoules into kilowatt-hours, reading a nutrition label in kilocalories and kJ, sizing an air-conditioner in BTU, or checking a physics figure in joules, foot-pounds or MeV. Every factor here is exact or a sourced standard (1 kWh = 3,600,000 J = 3.6 MJ; 1 kcal = 4,184 J; 1 BTU ≈ 1,055.06 J; 1 ft·lbf ≈ 1.3558 J; 1 MeV = 1.602176634 × 10⁻¹³ J), so the live tool and the numbers on every page below always agree.
Energy, not power. These pages live under /power/ for historical
reasons, but every unit here measures energy (work or heat), not power. Power is
energy per unit time — measured in watts (1 W = 1 J/s) — which is a different quantity.
Torque vs energy. The newton-metre (N·m) and foot-pound (ft·lbf) are used both for energy and for torque (a twisting force). The conversion number is the same either way (1 lbf·ft = 1.3558 N·m, just as 1 ft·lbf of energy = 1.3558 J), but the two are distinct physical quantities — a torque does not convert into kWh or calories. The relevant pages explain this where it matters.
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Units in this converter
| Unit | What it is |
|---|---|
| Joule (J) | The joule is the SI unit of energy — the work done by a force of one newton acting over one metre (1 J = 1 N·m), and also one watt-second. |
| Newton-metre (N·m) | A newton-metre is one newton applied over one metre. As a unit of ENERGY it is identical to the joule (1 N·m = 1 J); as a unit of TORQUE it measures rotational effort — a different physical quantity that does not convert into joules, kWh or calories. |
| Kilojoule (kJ) | A kilojoule is 1,000 joules — the energy unit on food labels (shown next to kilocalories) and for everyday amounts of energy. |
| Megajoule (MJ) | A megajoule is 1,000,000 joules (1,000 kJ) — used for larger energy quantities such as the energy content of fuels. |
| Watt-hour (Wh) | A watt-hour is the energy of one watt sustained for one hour — exactly 3,600 joules. Commonly used to rate battery capacity. |
| Kilowatt-hour (kWh) | A kilowatt-hour is 1,000 watt-hours — exactly 3,600,000 joules (3.6 MJ). It is the "unit" your electricity meter bills. |
| Megawatt-hour (MWh) | A megawatt-hour is one million watt-hours — 3.6 × 10⁹ joules (3,600 kWh). Used for power-station output and grid-scale energy. |
| Foot-pound (ft·lbf) | A foot-pound is the energy of one pound-force acting over one foot — about 1.3558 joules. The same number (as the pound-foot, lbf·ft) is also the common US unit of TORQUE. |
| Megaelectronvolt (MeV) | A megaelectronvolt is the energy an electron gains across a one-million-volt potential — 1 MeV = 1.602176634 × 10⁻¹³ J (the elementary charge is exact since the 2019 SI redefinition). Standard in nuclear and particle physics. |
| Calorie (cal) | A (small/gram) calorie is roughly the heat needed to raise 1 g of water by 1 °C — the thermochemical calorie is exactly 4.184 J. The food "Calorie" is actually a kilocalorie. |
| Kilocalorie (kcal) | A kilocalorie (the food "Calorie", Cal) is 1,000 small calories — exactly 4,184 J. It is the energy figure printed on nutrition labels. |
| British Thermal Unit (BTU) | A British thermal unit is roughly the heat needed to raise one pound of water by 1 °F — about 1,055.06 J (the International Table BTU). Common in heating, cooling (AC tonnage) and US energy work. |