Why is the calorie on food labels not the same as the chemistry calorie?

Food 'Calories' (capital C) = kilocalories (kcal). Chemistry uses lowercase 'calorie' (cal) = 1/1000 kcal. When you see 100 calories on a snack label, it's actually 100 kcal = 418 kJ.

I see a nutrition label with 2,500 kJ. How many calories is that?

Divide kJ by 4.184: 2,500 ÷ 4.184 = 598 kcal. So that food has about 600 calories (food Calories).

My fitness app shows 150 kcal burned. How many kJ is that?

150 × 4.184 = 628 kJ. If your app lets you toggle units, it should convert automatically. The energy burned is the same; it's just a different way to measure it.

Do I need to convert kcal to kJ for diet tracking?

No. Pick one system and stick with it (usually whatever your app uses). Conversions are mainly for reading international food labels or comparing studies. If working with small calorie units (not food Calories), see [calories to joules](/energy/calories-to-joules/) instead.

Kilocalories (kcal) to Kilojoules (kJ) Converter

Enter a value to instantly convert between energy units.

From

Precision4 dp

1 Kilocalorie = 4.184 Kilojoule

Key Formulas

Kilocalorie → Kilojoule

kJ = kcal × 4.184

Kilojoule → Kilocalorie

kcal = kJ × 0.239006

Kilowatt-Hour → Joule

J = kWh × 3600000

Joule → Kilowatt-Hour

kWh = J × 2.77778e-7

Formula

kJ = kcal × 4.184

Food calories (kcal) are used on nutrition labels in the US. Kilojoules (kJ) are the SI standard, used on labels worldwide (EU, UK, Australia, Canada). The calorie unit was originally defined as the energy to heat 1 gram of water by 1°C. One food 'Calorie' (with capital C) is actually 1 kilocalorie (kcal). For the reverse conversion, see [kilojoules to kilocalories](/energy/kj-to-kcal/).

Source: ISO 80000-5:2019 (Quantities and units—Thermodynamics)

Frequently Asked Questions

Real-World Examples

Medium apple or banana. A typical medium fruit has 80-100 kcal on US labels; 300-420 kJ internationally.

200 kcal = 837 kJ

Lunch meal energy. A balanced lunch (sandwich + fruit + drink) is roughly 500-700 kcal, or 2,100-2,900 kJ.

500 kcal = 2092 kJ

Daily caloric intake. 2,000 kcal is the reference daily intake on US nutrition labels. Internationally: 8,400 kJ.

2000 kcal = 8368 kJ

Definition. By scientific definition, 1 food calorie (kcal) = 4,184 joules = 4.184 kJ.

1 kcal = 4.184 kJ

kj to kcal kwh to joules joules to kwh btu to joules calories to joules

Kilocalories (kcal) to Kilojoules (kJ) Converter

Key Formulas

Formula

Frequently Asked Questions

Real-World Examples

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