Energy Converter
Convert joules, calories, kWh, BTU, and therms with exact factors.
What it does
Energy conversion multiplies by fixed factors between unit systems. The joule anchors science work, the kilowatt hour anchors electricity bills, the BTU anchors heating in the US, and the kilocalorie anchors food labels, so moving between them is daily math.
The tool above converts between eight units: joules, kilojoules, calories, kilocalories, watt hours, kilowatt hours, BTU, and therms. Pick both ends, enter the value, and every equivalent appears below the main answer.
Watch the calorie trap: physics calories are small, while food Calories with a capital C are kilocalories, one thousand times larger. A 500 kcal meal is 500,000 physics calories and about 2.092 megajoules.
Factors here follow NIST SI definitions and the EIA energy calculator references: 1 cal is 4.184 J exactly, 1 kWh is 3,600,000 J, and 1 BTU is about 1055.06 J.
How to use
- Enter the energy value in the source unit.
- Pick the source unit on the left and the target on the right.
- Read the converted line first.
- Scan the all units note for the rest of the equivalents.
- Keep food kcal separate from physics cal when logging diets.
Formula
- 3600000
- Joules in one kilowatt hour.
- 1055.05585262
- Joules in one BTU (59 F basis).
- 4184
- Joules in one kilocalorie (1000 small calories).
BTU definitions vary slightly by temperature basis, which shifts the fourth decimal. Bill math uses the values here consistently, so pairs stay exact within the page.
Worked example
Example: 1 kWh to BTU
Value 1, from kilowatt hours, to BTU.
- Joules first: 1 x 3600000 = 3600000 J.
- Divide by BTU factor: 3600000 / 1055.05585262 = 3412.1416.
- Result: 1 kWh = 3412.1416 BTU.
- Food check: 1 kWh / 4184 = 860.42 kcal.
- Reverse: 3412.1416 x 1055.05585262 / 3600000 = 1.0000 kWh.
Reference table
| Pair | Factor | Everyday check |
|---|---|---|
| 1 kWh to BTU | 3412.1416 | Heater hour is about 3412 BTU |
| 1 kcal to kJ | 4.184 | 500 kcal meal is 2092 kJ |
| 1 therm to kWh | 29.3072 | Gas therm is near 29.3 kWh |
| 1 BTU to J | 1055.0559 | Match head is about 1 BTU |
| 1000 BTU to kWh | 0.29307 | Small AC moves this per hour |
Limits
- Energy only. Power divides by time and needs the electricity page.
- BTU bases vary by standard, shifting late decimals.
- Food energy metabolizes below bomb calorimeter values.
- Billing adds fixed charges and tiers beyond raw units.
Common mistakes
- Logging food kcal as small cal, understating by 1000 times.
- Using 1000 instead of 1024 style mixes from data units.
- Rounding mid chain across fuel to electricity steps.
- Reading BTU per hour as BTU total energy.
- Trusting remembered 3412 without the decimals for large plants.
Try it yourself
Quick checks. Answers sit tucked under each question.
500 kcal in kJ?
500 x 4.184 = 2092 kJ.
2 kWh in BTU?
2 x 3412.1416 = 6824.2832 BTU.
1 therm in kWh?
105506000 / 3600000 = 29.3072 kWh.
Questions
How many BTU in a kWh?
3412.1416 BTU. Multiply kWh by this to price heat against electricity.
Food calorie vs physics calorie?
Labels use kcal (1000 small calories). A 500 kcal meal is 2092 kJ.
What is a therm?
100,000 BTU, about 29.3 kWh, the common US gas billing block.
Joules or kWh for bills?
Bills use kWh (millions of joules) to keep numbers small: 1 kWh is 3.6 MJ.
Why does BTU vary?
Its definition depends on which degree Fahrenheit warms the pound of water. Standards differ in late decimals.
Which unit for diet math?
Kilocalories on labels and kilojoules in science texts. Convert with 4.184.