Convert joules, calories, kilowatt-hours and BTU with exact defined factors and everyday reference amounts, in your browser. Runs entirely in your browser — your numbers never leave this device.
| Unit | Value |
|---|---|
| Joules (J) | 3,600,000 J |
| Kilojoules (kJ) | 3,600 kJ |
| Calories (thermochemical) (cal) | 860,420.650096 cal |
| Kilocalories (kcal) | 860.42065 kcal |
| Watt-hours (Wh) | 1,000 Wh |
| Kilowatt-hours (kWh) | 1 kWh |
| British thermal units (BTU) | 3,412.141633 BTU |
| Foot-pounds (ft·lb) | 2,655,223.737398 ft·lb |
| Unit | Joules |
|---|---|
| Joule (J) | 1 |
| Calorie (cal) | 4.184 |
| Kilojoule (kJ) | 1,000 |
| Kilocalorie (kcal) | 4,184 |
| Watt-hour (Wh) | 3,600 |
| British thermal unit (BTU) | 1,055.05585262 |
| Kilowatt-hour (kWh) | 3,600,000 |
The joule is the base unit, and the others are defined against it: 1 calorie = 4.184 J exactly, so a food Calorie — which is really a kilocalorie — is 4,184 J. A kilowatt-hour is the energy of 1,000 watts running for 3,600 seconds, so 1 kWh = 3.6 megajoules exactly. A British thermal unit is defined here as 1,055.05585262 J, the International Table BTU used in most engineering work.
Food energy is the everyday trap: labels that say Calories, with a capital C in US practice, mean kilocalories. A 2,000 kcal day is therefore 2,000 × 4,184 = 8,368,000 J = 8.368 MJ, and in electrical units that is 8,368,000 ÷ 3,600,000 = 2.32 kWh. Entering 2,000 small calories instead would understate the day's energy by a factor of 1,000.
For scale, a single AA alkaline cell stores roughly 2.6 amp-hours at 1.5 volts, which is about 3.9 watt-hours or 3.9 × 3,600 = 14,040 J (14.04 kJ). That figure is an estimate from typical cell capacity, unlike the unit factors themselves, which are exact definitions — the examples keep the two kinds of number clearly separate.
No — a food Calorie is a kilocalorie, 1,000 small calories, equal to 4,184 J. Food labels in many countries print kcal directly, which avoids the ambiguity. This converter lists cal and kcal as separate units so a diet figure is never out by a factor of 1,000.
3,600,000 ÷ 1,055.05585262 = 3,412.14 BTU. That is why a heater rated at 10,000 BTU per hour is roughly a 2.93 kW heater: 10,000 × 1,055.05585262 ÷ 3,600,000 = 2.9307 kW of power over the hour.
A kilowatt is power — the rate of using energy — while a kilowatt-hour is energy itself: one kilowatt sustained for one hour, equal to 3.6 MJ. This converter handles energy units (J, kcal, BTU, kWh). To turn a kWh figure into an average power, divide by the number of hours it was used over.
The International Table BTU, defined as 1,055.05585262 J. Slightly different BTU definitions exist for specific industries, differing by well under 0.1%, so for heating and appliance conversions the International Table value is the standard choice.
Roughly 14 kJ, as an estimate: a typical alkaline AA delivers about 2.6 Ah at 1.5 V, which is about 3.9 Wh, and 3.9 × 3,600 = 14,040 J. Actual capacity varies by brand, age and how fast the energy is drawn, so treat it as a scale reference rather than a specification.
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