Kilocalories to Kilojoules Converter

Many food labels print energy in both kilojoules and kilocalories, and some print only kJ. This page treats the number you type as kilocalories, the unit people mean when they say a snack has 250 calories, and multiplies by 4.184:

Converting a label's kcal figure will not always land exactly on the kJ figure printed beside it. Each number on a label is usually rounded on its own, so a few kJ of difference is normal and does not mean the converter or the label is wrong.

The practical use is putting two sources on the same scale: a recipe app that logs kcal against a label that only shows kJ, or a meal plan written in one unit while your tracker uses the other. Pick one unit and convert everything into it before adding up. Adding a kJ figure to a kcal figure is an easy way for a daily total to end up badly wrong, because the kJ number is about four times larger.

Going the other way, use the swap button. A product listing 8700 kJ is 2079.35 kcal.

Labels often give energy per 100 g as well as per serving, so check which column you are converting. 180 kcal per 100 g is 753.12 kJ per 100 g; a 30 g serving of the same food is 54 kcal, or 225.94 kJ.

The exact factor is 4.184. Rounding it to 4.2 is only 0.38% high: 250 kcal × 4.2 = 1050 kJ against 1046. Multiplying by 4 is simpler but 4.4% low, which is 46 kJ short at 250 kcal. A good compromise is to multiply by 4 and add 5%: 1000 + 50 = 1050.

Some books write food energy as Calories with a capital C to mean kilocalories, and use calories with a small c for the unit that is a thousand times smaller. This page's From unit is the big one. If your number comes from a physics or chemistry problem in small calories, switch the From menu to Calorie (cal) first. Then 250 cal is 1.046 kJ, not 1046.