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How Many Calories in Onion?
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Quick reference — common serving sizes
| Amount | Calories | Protein |
|---|---|---|
| 1 oz (28g) | 11 kcal | 0.3g |
| 100g | 40 kcal | 1.1g |
| 1 medium onion | 44 kcal | 1.2g |
A onion contains 40 calories per 100g. A typical 1 medium onion (110g) provides about 44 calories. Onion is low in calories. Accurate tracking starts with weighing portions — a digital kitchen scale removes all the guesswork.
Onion Nutrition Facts
| Nutrient | Per 100g | Per serving (110g) |
|---|---|---|
| Calories | 40 kcal | 44 kcal |
| Protein | 1.1g | 1.2g |
| Carbohydrates | 9.3g | 10.2g |
| of which Sugars | 4.2g | 4.6g |
| Fat | 0.1g | 0.1g |
| of which Saturates | 0.0g | 0.0g |
| Fibre | 1.7g | 1.9g |
| Sodium | 4.0mg | 4mg |
| Potassium | 146.0mg | 161mg |
| Calcium | 23.0mg | 25mg |
| Iron | 0.2mg | 0.2mg |
| Vitamin C | 7.4mg | 8.1mg |
| Vitamin A | 0.0µg | 0µg |
| Selenium | 0.5µg | 1µg |
| Riboflavin (B2) | 0.0mg | 0.0mg |
% of Daily Value (per 100g)
Based on a standard 2,000-calorie reference diet — the same basis used on nutrition labels in the US and UK.
- Low in saturated fat (0% DV)
- Low in sodium (0% DV)
- Calories: 2% DV
- Protein: 2% DV
- Carbohydrates: 3% DV
- Fibre: 6% DV
- Fat: 0% DV
- Saturated fat: 0% DV
- Sodium: 0% DV
- Potassium: 3% DV
- Calcium: 2% DV
- Iron: 1% DV
- Vitamin C: 8% DV
- Vitamin A: 0% DV
- Selenium: 1% DV
- Riboflavin (B2): 0% DV
Useful for tracking onion
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Have a cat or dog? Check whether onion is safe for your dog or safe for your cat before sharing. Also check the full ingredient breakdown and food safety guide for pregnancy and storage advice. Use a meal prep container set to portion out onion for the week. Tracking supplements too? Check drug and supplement interactions before combining anything new.
Good to know
Cooking method matters here too — boiling can leach some water-soluble vitamins into the cooking water, while steaming or roasting tends to retain more.
Does onion fit your diet?
Weight management
At 40 calories per 100g, onion is calorie-light relative to its volume, which can help keep a meal within a calorie target without needing very small portions.
Frequently Asked Questions
How many calories in onion per 100g?
Onion contains 40 calories per 100g, based on USDA reference data.
Is onion high in calories?
A 1 medium onion of onion (110g) has around 44 calories — roughly 2% of a 2,000-calorie daily intake.
Is onion good for weight loss?
At 40 calories per 100g, onion is relatively low in calories and can fit well into a weight-loss diet. A 1 medium onion provides about 44 calories.
How much protein is in onion?
Onion contains 1.1g of protein per 100g.
Is onion a good source of fibre?
Onion is relatively low in fibre at 1.7g per 100g, so pairing it with fibre-rich sides (vegetables, whole grains, legumes) can help balance a meal.
How does onion compare to beans, snap, green, frozen?
Onion has 40 calories per 100g, close to beans, snap, green, frozen at 40 — 0 calories fewer per 100g. See the full macro breakdown above.
How many servings of onion for 20g of protein?
With 1.1g of protein per 100g, you'd need roughly 1818g of onion to reach 20g of protein
Foods with a similar calorie count
Other vegetables closest to onion by calories per 100g:
| Food | Calories | Protein | Carbs | Fat |
|---|---|---|---|---|
| Onion (this page) | 40 kcal | 1.1g | 9.3g | 0.1g |
| Beans, Snap, Green, Frozen | 40 kcal | 2.0g | 7.0g | 0.4g |
| Squash, Winter, Acorn, Raw | 40 kcal | 0.8g | 10.4g | 0.1g |
| Squash, Winter, Butternut, Cooked | 40 kcal | 0.9g | 10.5g | 0.1g |
| Squash, Winter, Hubbard, Raw | 40 kcal | 2.0g | 8.7g | 0.5g |
| Tree Fern, Cooked, without Salt | 40 kcal | 0.3g | 11.0g | 0.1g |
| Carrot Juice, Canned | 40 kcal | 0.9g | 9.3g | 0.1g |
More kit for onion tracking
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Nutrition data: USDA FoodData Central (public domain, CC0 1.0). Values are per 100g unless stated.