How Many Calories in an Onion? Nutrition Facts & Macros
One medium onion (110g) has 44 calories
Protein 1.2g · Carbs 10.3g · Fat 0.1g
Onions are a kitchen staple used in almost every cuisine — adding flavor, aroma, and surprisingly also nutrients. Whether you use them as a base for dishes, in salads, or track your macros, knowing the exact nutrition facts helps. Here's everything you need to know about onion calories and macros, based on USDA data. Raw onions are about 89% water.
167 kJ · per 100g · Water: 89.11 g
Calorie Calculator: Onion (Raw)
110 g Onion (Raw) contains 44 kcal
Calories by Portion Size
| Portion | Calories | Protein | Carbs | Fat |
|---|---|---|---|---|
| 1 medium onion (110g) | 44 kcal | 1.2g | 10.3g | 0.1g |
| 1 cup chopped (160g) | 64 kcal | 1.8g | 14.9g | 0.2g |
| 100 grams | 40 kcal | 1.1g | 9.3g | 0.1g |
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Onion (Raw) — Nutrition Facts
| Onion (Raw) | per 100g |
|---|---|
| Calories | 40 kcal |
| Protein | 1.1 g |
| Fat | 0.1 g |
| Carbs | 9.34 g |
| Fiber | 1.7 g |
| Sugar | 4.24 g |
| Sodium | 4 mg |
| Potassium | 146 mg |
| Phosphorus | 29 mg |
| Vitamin C | 7.4 mg |
| Folate | 19 mcg |
| Water | 89.11 g |
Source: USDA FoodData Central (FDC ID: 170000) · Data verified April 2026
Variations
Red onion
About 40 kcal per 100g — same calories as yellow onion. Protein 1.1g, carbs 9.34g, fat 0.1g per 100g. Higher in antioxidants (anthocyanins). Milder flavor, popular raw in salads and on burgers.
Sweet onion
About 32 kcal per 100g — fewer calories than yellow onion. Protein 0.8g, carbs 7.55g, fat 0.08g per 100g. Higher water content, milder and sweeter taste. Popular for onion rings, caramelizing, and eating raw.
Spring onion (scallion)
About 32 kcal per 100g — fewer calories than yellow onion. Protein 1.83g, carbs 7.34g, fat 0.19g per 100g. Higher in vitamin A and vitamin K. Milder flavor, used as garnish and in Asian cuisine.
Dietary Perspectives
For Weight Loss
At 40 kcal per 100 g, onion is a low-calorie vegetable. It contains 1.7 g of fiber and 89.1% water. Used primarily as a flavoring ingredient — adds significant taste for minimal calories. A medium onion (~110 g, ~44 kcal) used in cooking distributes across a whole dish. Sugar content is 4.2 g per 100 g, mostly caramelizing sugars that develop during cooking.
For Athletic Performance
Onion provides 9.3 g of carbohydrates per 100 g — used mainly as a flavoring, not a fuel source. Contains 146 mg of potassium per 100 g. Research shows quercetin in onions may have mild anti-inflammatory effects. Not a performance food but a valuable cooking ingredient for nutrient-dense athlete meals.
For Keto
Moderately keto-friendly when used in cooking quantities. Raw onion has 7.6 g of net carbs per 100 g (9.3 g total carbohydrates minus 1.7 g fiber). A quarter onion (~28 g, ~2.1 g net carbs) used in a recipe is manageable. Avoid large portions of raw onion (e.g., onion rings) which can accumulate significant carbs.
Frequently Asked Questions
How many calories are in an onion?
One medium raw onion (110g) contains approximately 44 calories. Per 100g, raw onions have 40 calories. A cup of chopped onion (160g) has about 64 calories. Onions are relatively low in calories for the amount of flavor they add to dishes.
How many carbs are in an onion?
Per 100g, raw onions contain 9.34g of carbohydrates, of which 4.24g is sugar and 1.7g is fiber. One medium onion (110g) has about 10.3g of carbs. Onions are moderate in carbs — higher than most leafy vegetables but lower than potatoes (17.49g per 100g). They're used in small amounts in keto cooking.
How much sugar is in an onion?
Onions contain 4.24g of sugar per 100g — surprisingly high for a vegetable that doesn't taste sweet when raw. One medium onion (110g) has about 4.7g of sugar. When caramelized, the sugars concentrate and become more apparent. Sweet onions have even more sugar (~5.0g per 100g).
Raw onion vs cooked onion — what's the difference?
Raw onion: 40 kcal, 9.34g carbs per 100g. Sauteed onion: about 44 kcal per 100g (slightly more due to water loss and oil). Caramelized onions are much more calorie-dense because water evaporates and sugars concentrate. Raw onions retain more vitamin C and quercetin (antioxidant). Cooking makes onions sweeter and milder.
How much vitamin C is in an onion?
Raw onions contain 7.4mg of vitamin C per 100g — about 8% of the daily recommended intake. One medium onion (110g) provides about 8.1mg. While not a primary vitamin C source, onions contribute when eaten regularly. Cooking reduces vitamin C content significantly.
Are onions good for weight loss?
Onions are a helpful addition to a weight loss diet. At 40 calories per 100g, they add massive flavor to meals without many calories. One medium onion has only 44 calories. They contain 1.7g of fiber and 89% water. Using onions in soups, stir-fries, and salads helps make low-calorie meals more satisfying and flavorful.
Compare with Similar Foods
| Portion | kcal | Protein | Carbs | Fat |
|---|---|---|---|---|
| Onion (Raw) | 40 | 1.1g | 9.34g | 0.1g |
| Tomato | 18 | 0.88g | 3.89g | 0.2g |
| Carrot | 41 | 0.93g | 9.58g | 0.24g |
| Mushrooms (White) | 22 | 3.09g | 3.26g | 0.34g |
| Cabbage (Green) | 25 | 1.28g | 5.8g | 0.1g |
per 100g
One medium onion has 44 kcal (110g). At 40 kcal per 100g, onions have more calories than most vegetables like cabbage (25 kcal) and tomatoes (18 kcal), but add significant flavor for a modest calorie cost.
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