To convert gigajoules to calories, multiply by 239,005,736.1. That factor is the whole relationship: both units measure energy, so the conversion is a proportion with no offset and no substance-specific constant.
The unit district heating and industrial gas contracts are billed in. The small or gram calorie — 1/1000 of the dietary Calorie.
The calorie problem. A dietary Calorie is a kilocalorie, one thousand of the calories physics uses, so a 250 Calorie snack is 250,000 cal or 1,046 kJ. Food labels outside the US print kilojoules for exactly this reason. Below the calculator there is a step table for the values people look up most, and a second table putting real energy figures into calories so the number you get has something to be compared against.
The formula
gigajoules- The amount you are converting, in gigajoules
239,005,736.138- The exact number of calories in one gigajoule
calories- The converted result
How it works, step by step
- Enter the value in gigajoules.
- It is multiplied by 239,005,736.138, the exact factor between the two units.
- The answer is shown in calories, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
An hour of a 2 kW heater: 0.0072 GJ in calories
Take an hour of a 2 kw heater, roughly 0.0072 GJ. The conversion is a single multiplication — 0.0072 × 2.39006e+08 — giving 1.72084e+06 cal. Because the relationship is proportional, doubling the input doubles the answer to 3.44168e+06 cal.
A slice of bread: 0.000335 GJ in calories
At 0.000335 GJ (a slice of bread), the same quantity in calories is 0.000335 × 2.39006e+08 = 80,066.9 cal. One gigajoule is 2.39006e+08 calories, so the numbers grow as expected.
How to read your score
Frequently asked questions
How many calories are in one gigajoule?
Exactly 239,005,736.138. Every figure on this page is that one number multiplied by your input, so the only rounding is at the display step.
What is the formula to convert gigajoules to calories?
calories = gigajoules × 239,005,736.138. Reversed, gigajoules = calories ÷ 239,005,736.138, which is the same as multiplying by 4.184e-09.
Which is the bigger unit, the gigajoule or the calorie?
The gigajoule. One gigajoule equals 2.39006e+08 calories.
What does this quantity actually measure?
Both units measure energy. That is why a single factor is enough: there is no temperature offset and no material property involved, unlike conversions that cross between different quantities.
What is a gigajoule?
The unit district heating and industrial gas contracts are billed in.
What is a calorie?
The small or gram calorie — 1/1000 of the dietary Calorie.
Why does my answer differ from another converter?
Almost always because the other tool rounded the factor before multiplying. This page keeps full double precision through the calculation and rounds only for display, and it prints the factor it used so you can see where any difference came from.
Is there a quick way to do GJ to cal in my head?
Plenty of people do this in their head: multiply by 240000000.000000 instead of using the exact factor 239,005,736.1. At 100 that shortcut gives 24000000000.000000 calories, off by 99426386.233269 calories or about 0.42%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Gigajoules to calories reference tables
| Gigajoules | Calories |
|---|---|
| 0.5 GJ | 1.19503e+08 cal |
| 1 GJ | 2.39006e+08 cal |
| 2 GJ | 4.78011e+08 cal |
| 3 GJ | 7.17017e+08 cal |
| 5 GJ | 1.19503e+09 cal |
| 10 GJ | 2.39006e+09 cal |
| 20 GJ | 4.78011e+09 cal |
| 25 GJ | 5.97514e+09 cal |
| 50 GJ | 1.19503e+10 cal |
| 75 GJ | 1.79254e+10 cal |
| 100 GJ | 2.39006e+10 cal |
| 250 GJ | 5.97514e+10 cal |
| 500 GJ | 1.19503e+11 cal |
| 1000 GJ | 2.39006e+11 cal |
| 5000 GJ | 1.19503e+12 cal |
Exact factor: 1 gigajoule = 239,005,736.138 calories.
| Quantity | GJ | cal |
|---|---|---|
| A AA battery | 1.296e-05 GJ | 3098 cal |
| A slice of bread | 0.0003347 GJ | 8e+04 cal |
| A phone battery charge | 4.104e-05 GJ | 9809 cal |
| An hour of a 2 kW heater | 0.0072 GJ | 1.721e+06 cal |
| A day of household electricity | 0.036 GJ | 8.604e+06 cal |
| A litre of petrol | 0.0342 GJ | 8.174e+06 cal |
Published reference values, converted with the same factor this page uses.