TempoLife › Calorie database › Vegetables › Onion
Onion calories and nutrition facts
100 grams of onion contains 40 calories, with 1.1 g of protein, 9.3 g of carbohydrate and 0.1 g of fat. It provides 1.7 g of fiber and 4.2 g of sugar per 100 g. Most of its calories come from carbohydrate.
Onions are a flavour base, not an energy source — a whole medium onion is around 45 calories, and most of a dish's "onion" calories actually come from the fat it was softened in. Caramelising drives off water and concentrates sweetness without adding energy. Log the oil honestly and the onion generously.
Where the calories come from
Protein 10% Carbs 88% Fat 2%
How onion compares
Per 100 g, against the closest vegetables in this database.
| Food | Calories | Protein | Carbs | Fat |
|---|---|---|---|---|
| Onion | 40 kcal | 1.1 g | 9.3 g | 0.1 g |
| Red onion | 40 kcal | 1.1 g | 9.3 g | 0.1 g |
| Carrot juice, canned | 40 kcal | 1 g | 9.3 g | 0.2 g |
| Carrot | 41 kcal | 0.9 g | 9.6 g | 0.2 g |
| Frozen butternut squash, cooked | 39 kcal | 1.2 g | 10.1 g | 0.1 g |
Nutrition facts for onion
| Nutrient | Per 100 g | Per 1 medium onion |
|---|---|---|
| Calories | 40 kcal | 44 kcal |
| Protein | 1.1 g | 1 g |
| Carbohydrate | 9.3 g | 10 g |
| Fat | 0.1 g | 0 g |
| Fiber | 1.7 g | 2 g |
| Sugar | 4.2 g | 5 g |
| Saturated fat | 0 g | 0 g |
| Salt | 0 g | 0 g |
Print an EU-style nutrition label for onion — per 100 g and per portion.
Vitamins and minerals in onion
Per 100 g, highest share of the Daily Value first. %DV = the adult Daily Value (FDA reference). USDA reference data — not medical advice.
| Nutrient | Per 100 g | %DV |
|---|---|---|
| Vitamin C | 7.4 mg | 8% |
| Vitamin B6 | 0.12 mg | 7% |
| Manganese | 0.13 mg | 6% |
| Copper | 0.04 mg | 4% |
| Thiamin (B1) | 0.05 mg | 4% |
| Potassium | 146 mg | 3% |
| Calcium | 23 mg | 2% |
| Magnesium | 10 mg | 2% |
See the richest foods per nutrient in the nutrient toplists.
Calories in common onion servings
How many calories in a portion of onion — reference serving estimates with the gram weight shown.
| Serving | Calories | Protein | Carbs | Fat |
|---|---|---|---|---|
| 1 slice, thin (9 g) | 3.6 kcal | 0.1 g | 0.8 g | 0 g |
| 1 slice, medium (14 g) | 5.6 kcal | 0.2 g | 1.3 g | 0 g |
| 1 slice, large (38 g) | 15 kcal | 0 g | 4 g | 0 g |
| 100 g (100 g) | 40 kcal | 1 g | 9 g | 0 g |
| 1 cup, sliced (115 g) | 46 kcal | 1 g | 11 g | 0 g |
Log onion in one tap
TempoLife lets you search this food, pick your portion and save it to a private daily diary — or snap a photo of the whole meal and edit the estimate. Free to start.
Frequently asked questions
How many calories are in onion?
Onion has 40 calories per 100 grams. A typical serving of 1 medium onion (110 g) has about 44 calories.
How much protein is in onion?
Onion contains 1.1 g of protein per 100 g, or about 1 g per 1 medium onion.
How much sugar is in onion?
Onion contains 4.2 g of sugar per 100 g. Nutrition values are reference figures; brands and preparation change the real amount, so weigh and log what you actually eat.
Are these onion calories exact?
No. These are per-100-gram reference values from the USDA FoodData Central SR Legacy source family. Portion size, ripeness, cut and cooking method all change the real number, so treat them as an estimate and log your own portion.
Related foods
Source: USDA FoodData Central SR Legacy #170000 (2018-04 release). US Government work — public domain in the United States. Reference values per 100 g edible portion.
