Convert energy between joules, kilojoules, kilowatt-hours, calories, kilocalories (food calories) and BTU — with exact factors.
What Is an Energy Converter?
An energy converter translates between energy’s many units: 1 kWh = 3,600 kJ = 860.421 kcal; 1 BTU = 1.0551 kJ. Electricity bills use kWh, food labels use kcal (“calories”), heating uses BTU, and physics uses the joule. The food “calorie” is really a kilocalorie (1,000 small calories) — the capital-C Calorie — which is why a 2,000 kcal diet is 8,368 kJ of energy.
How to Use
- Enter the value.
- Pick the “from” unit.
- Pick the “to” unit.
- Click “Convert Energy”.
Formula
Convert to joules first (value × from-factor), then divide by the to-factor. All factors are exact definitions.
Worked Example
1 kWh → kJ: 3,600,000 ÷ 1,000 = 3,600 kJ. And 1 BTU → kJ: 1,055.05585262 ÷ 1,000 = 1.0551 kJ.
How It Works, In Plain Words
Every unit is stored as its value in joules: the joule is 1, the kilojoule 1,000, the calorie 4.184, the kilocalorie 4,184, the BTU 1,055.05585262 and the kilowatt-hour 3,600,000. The tool multiplies your value by the from-factor to reach joules, then divides by the to-factor — the worked example runs both halves, turning 1 kWh into 3,600,000 ÷ 1,000 = 3,600 kJ, and 1 BTU into 1,055.05585262 ÷ 1,000 = 1.0551 kJ. One shared scale in the middle is what keeps bills, food and heating speaking to each other.
The introduction’s headline row is the same arithmetic compressed: 1 kWh = 3,600 kJ = 860.421 kcal, and 1 BTU = 1.0551 kJ. It also maps the units to their homes — electricity bills use kWh, food labels use kcal, heating uses BTU and physics uses the joule — so the dropdown is really four different worlds sharing one scale. Results are shown to four decimal places, which is how the BTU keeps its long factor’s precision instead of being rounded into a rough guess.
Real-World Uses
A householder reading an electricity bill in kWh converts a day’s usage into kilojoules to compare it with the kilocalorie figures food labels use — the introduction’s own bridge, since it points out that a 2,000 kcal diet is 8,368 kJ of energy. A cook or dieter working the other way turns a label’s kcal into kJ for a recipe or tracker that expects kilojoules, using the same 4,184-joule kilocalorie. A heating engineer sizing a system quoted in BTU converts the rating into kWh to set it beside the rest of the home’s electrical figures. Each task is one pass through joules, whichever world the paperwork came from. The converter exists because those worlds rarely print the same unit twice.
Benefits
- Six units covering bills, food, heating and physics
- The food-calorie vs kilocalorie trap explained
- Exact defined factors
- Both directions in one tool
Features of Our Tool
- Instant results in your browser
- No sign-up, no download, 100% free
- Works on mobile, tablet and desktop
- Clear step-by-step explanation below the tool
- Private — your entries never leave your device
Common Mistakes
- Confusing cal with kcal — food “calories” are kilocalories, 1,000× bigger
- Mixing energy (kWh) with power (kW) — one is the other times time
- Using BTU for cooling without noting it is an energy unit, not power
Common Mistakes to Avoid
The first mistake is confusing cal with kcal: the list warns that food “calories” are kilocalories, 1,000× bigger, and the introduction repeats that the food “calorie” is really 1,000 small calories — the capital-C Calorie — so picking cal instead of kcal shrinks a value a thousandfold. The second is mixing energy with power, since the list notes one is the other times time, and the FAQ spells it out: a 1 kW heater running 1 hour uses 1 kWh. The third is using BTU for cooling without noting it is an energy unit, not power, as the list puts it. Match the unit to the document in front of you before you convert.
FAQ
How many kJ in 1 kWh?
3,600 kJ.
How many kJ in 1 BTU?
1.0551 kJ.
Are food calories kilocalories?
Yes — the “calorie” on food labels is really a kilocalorie (1,000 small calories); 2,000 kcal = 8,368 kJ.
How many kcal in 1 kWh?
About 860.421 kcal.
What is the difference between kW and kWh?
kW is power (rate); kWh is energy (power × time) — a 1 kW heater running 1 hour uses 1 kWh.
How many joules are in 1 kilocalorie?
4,184 joules — the kilocalorie’s factor in this tool. That is also why the introduction’s 2,000 kcal diet works out to 8,368 kJ: 2,000 × 4,184 joules, expressed in kilojoules.
Can I convert kWh straight into kcal here?
Yes — both are on the dropdown, and the introduction gives the headline figure: 1 kWh = 860.421 kcal. The tool still routes through joules underneath, multiplying by 3,600,000 and dividing by 4,184.