Calories in Onion
Per 1 medium, 110 g
Onion has 44 calories per 1 medium, 110 g. That is about 2% of a 2,000-calorie day. The same serving provides 1.2 g of protein, 10.3 g of carbohydrate, 0.1 g of fat and 1.9 g of fibre. Per 100 g, that works out at 40 calories and 1.1 g of protein. Against the thresholds EU food labelling uses, it qualifies as fat free and low energy. Softening onions in stock rather than oil saves around 100 calories a pan.
Calories and macros
| Per 1 medium, 110 g | Serving | Per 100 g | % of daily intake |
|---|---|---|---|
| Calories | 44 kcal | 40 kcal | 2% |
| Protein | 1.2 g | 1.1 g | 2% |
| Carbohydrate | 10.3 g | 9.4 g | 4% |
| Fat | 0.1 g | 0.1 g | 0% |
| Fibre | 1.9 g | 1.7 g | 6% |
Daily intake percentages use the EU reference intakes an average adult label is based on: 2,000 kcal, 50 g protein, 260 g carbohydrate, 70 g fat, 30 g fibre.
What this is good for
These are the nutrition claims this food would qualify for under EU labelling rules — thresholds, not opinions.
Worth knowing
Figures are for a typical example and will vary by brand, ripeness and how it was cooked. For a target of your own, run the calorie calculator or take the short quiz. To log this without doing the arithmetic, Joules is free.
Figures last reviewed 29 August 2026.
Common questions about an onion
How many calories are in an onion?
Onion has 44 calories per 1 medium, 110 g, which is about 2% of a 2,000-calorie day.
How many calories are in 100 g of onion?
100 g of onion contains 40 calories.
How much protein is in an onion?
One serving of 1 medium, 110 g provides 1.2 g of protein — 1.1 g per 100 g, or 2% of the 50 g daily reference intake.
How many carbs are in an onion?
One serving of 1 medium, 110 g contains 10.3 g of carbohydrate, of which 1.9 g is fibre.
What is an onion a good source of?
Measured against EU food labelling thresholds, onion qualifies as fat free and low energy. Under 0.5 g of fat per 100 g. Under 40 calories per 100 g — a lot of food for very little.