Energy Converter
Convert between Joules, Kilojoules, Calories, Kilocalories, Watt-hours, kWh, BTU, Electronvolts, and Foot-pounds instantly.
Quick Reference
How to Convert Energy Units
Energy is the capacity to do work. This converter works by converting every input to the base unit (Joules), then to the target unit. Energy measurement is essential in physics, nutrition, electricity billing, and engineering.
Common Conversion Factors
| From | To | Multiply by |
|---|---|---|
| Kilowatt-hour | Joules | 3,600,000 |
| Kilocalorie | Joules | 4,184 |
| BTU | Joules | 1,055.06 |
| Calorie | Joules | 4.184 |
| Watt-hour | Joules | 3,600 |
| Foot-pound | Joules | 1.35582 |
| kWh | BTU | 3,412.14 |
Energy in Everyday Life
Food energy is measured in kilocalories (Calories). An average adult needs 2,000—2,500 kcal per day. Electricity is billed in kilowatt-hours — a typical US household uses about 900 kWh per month. Heating/cooling capacity is rated in BTU; a window AC unit might be rated at 8,000 BTU/hour.
Energy Quick Reference
| kWh | Joules | BTU | kcal |
|---|---|---|---|
| 0.001 | 3,600 | 3.41 | 0.860 |
| 1 | 3,600,000 | 3,412 | 860 |
| 10 | 36,000,000 | 34,121 | 8,598 |
| 100 | 360,000,000 | 341,214 | 85,985 |
| 1,000 | 3,600,000,000 | 3,412,142 | 859,845 |
What we mean by "energy"
Energy is the capacity to do work. The SI unit is the joule (J) — one newton applied through one metre. Outside of physics most people meet energy in three guises: food energy measured in kilocalories (kcal, often misleadingly called "Calories" with a capital C), electrical energy measured in kilowatt-hours (kWh) and shown on every electricity bill, and heating energy measured in BTU (British Thermal Units) which still dominates HVAC datasheets in the US. All three describe the same physical quantity using different reference scales.
Conversion factors that matter daily
| From | To | Multiply by |
|---|---|---|
| 1 kilowatt-hour (kWh) | joules | 3,600,000 |
| 1 kilowatt-hour | kilocalories | 860.4 |
| 1 kilocalorie (food Calorie) | joules | 4,184 |
| 1 BTU | joules | 1,055.06 |
| 1 BTU | kilocalories | 0.252 |
| 1 therm (gas billing unit) | kWh | 29.3 |
| 1 electronvolt (eV) | joules | 1.602 × 10⁻¹⁹ |
Worked example: how many "calories" in a kWh?
A 10-minute hot shower uses roughly 5 kWh of energy heating the water. Converted to food-energy units, that is 5 × 860 ≈ 4,300 kcal — more than two days of food intake for an average adult. The numbers feel surprising because we instinctively conflate "calories burned during exercise" with "energy used by an appliance"; they are the same physical units, applied to wildly different rates.
Common mistakes
- Mixing kcal and cal. The "Calorie" on a food label (capital C) means 1,000 chemistry-textbook calories — a kilocalorie. Most online converters silently default to the small calorie and produce wildly wrong food-energy answers.
- Confusing power and energy. A 1500 W kettle running for 4 minutes uses 100 Wh of energy. Power (W) is a rate; energy (Wh) is a quantity. Multiplying or dividing by time is what converts between them.
- Therm vs thermie. The US therm equals 100,000 BTU. The (now-obsolete) French thermie was 1 Mcal. Old recipes and engineering tables sometimes confuse the two.
- BTU on air-conditioner labels. Air-conditioner "12,000 BTU" ratings are actually BTU per hour — a unit of power, not energy.