Calories in onion

Raw. 40 kcal (167 kJ) per 100 g. Choose a portion below and every figure on the page updates.

Onions are mostly water and carbohydrate, giving raw onion 40 kcal (167 kJ) per 100 g. Almost half of the carbohydrate is natural sugar, which is why onions turn sweet when cooked slowly. They contain very little fat or protein and modest amounts of vitamin C, vitamin B6 and fibre, and are usually eaten in small quantities as a flavouring.

Where the energy comes from

Share of total energy contributed by each macronutrient, using the standard 4/4/9 kcal per gram factors:

Things worth knowing

• One medium onion (110 g) has about 44 kcal (184 kJ); a tablespoon of chopped onion is around 4 kcal (17 kJ), so onion used as seasoning adds very little.
• Frying is what changes the numbers. USDA's sautéed yellow onions have about 123 kcal per 100 g, roughly three times raw onion, almost entirely from the cooking fat.
• Boiled onions are almost identical to raw at about 44 kcal per 100 g, so cooking without fat makes little difference.
• The sweetness of caramelised onions comes from the onion's own sugars browning and concentrating as water cooks off, not from added sugar, unless a recipe includes it.

Converting these figures

One 1 medium onion of onion is 44 kcal, which is 184 kJ. To convert any other figure, divide kilojoules by 4.184 for calories, or use the converter on the home page.

It takes 598 g of onion to reach 1,000 kJ (239 kcal). See how that compares with other foods on the 1000 kJ to calories page.