How many calories in onion?
Per 100 g, onion provides about 40 kcal. But what matters is your real portion — and its size varies. Here are the reference values, common portions, and an honest range.
40–50 kcal · 1 onion1 onion (≈ 110 g) ≈ 44 kcal, i.e. a range of 40–50 kcal depending on size. A single to-the-gram number would be misleading.
Nutrition facts per 100 g
Calories per portion
Indicative reference values (e.g. ANSES Ciqual / USDA FoodData Central); real products vary.
Estimate onion from a photo, without weighing
With Volumeal, photograph your plate: onion is identified and its portion estimated, with a confidence range rather than a fake exact number. You can correct the portion in one tap to tighten the estimate.
To set your target, use the calorie calculator. For the full method, see how to count calories from a photo.
See also
Frequently asked questions
How many calories in 1 onion?＋
About 44 kcal (1 onion, ≈ 110 g), with a range of 40 to 50 kcal depending on real size.
What is the value per 100 g of onion?＋
About 40 kcal per 100 g, with 1.1 g protein, 9 g carbs and 0.1 g fat (reference values).
Do I need to weigh this food?＋
No: photograph your meal with Volumeal and the portion is estimated for you, with a confidence range.