Onion Calories & Carbs
Keto-friendlyLast updated September 8, 2026 · Compiled by the CarbMeNot Team
Values per 1 medium onion (110g); per 100 g: 7.7g net carbs, 40 cal. Net carbs = total carbs − fiber − sugar alcohols — do the math for any label with the free net carbs calculator.
How many carbs are in onion?
Onion — 1 medium onion (110g) — has 8.5g net carbs: 10.3g total carbs minus 1.9g fiber, plus 1.2g protein, 0.1g fat, and 44 calories. Per 100g that is 7.7g net carbs (9.4g total carbs, 1.7g fiber) and 40 calories. That makes onion relatively low in net carbs and lower than the typical vegetable, which averages about 17.9g net carbs per 100g. With this carb count, onion fits a keto or low-carb diet (usually 20–50g net carbs per day) in normal portions. Values are per 100 g, sourced from Open Food Facts; net carbs are computed by CarbMeNot.
Is onion keto-friendly?
Onion is borderline for keto — it works only in small portions. 1 medium onion (110g) is 8.5g net carbs (10.3g total carbs − 1.9g fiber); per 100g that is 7.7g net carbs. On a standard keto diet (20–50g net carbs per day), even one serving uses a large share of your daily carbs, so keep portions small or save it for a higher-carb day.
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Carbs by serving size
| Serving | Net carbs | Total carbs | Protein | Calories |
|---|---|---|---|---|
| 1 medium onion | 8.5g | 10.3g | 1.2g | 44 |
| 100 g (3.5 oz) | 7.7g | 9.4g | 1.1g | 40 |
| 1 oz (28 g) | 2.2g | 2.6g | 0.3g | 11 |
How many calories are in onion?
Onion — 1 medium onion (110g) — has 44 calories, with 1.2g protein, 0.1g fat, and 8.5g net carbs. Per 100g: 40 calories and 7.7g net carbs.
Nutrition facts
| Nutrient | Amount (per 100 g) |
|---|---|
| Calories | 40 |
| Total carbs | 9.4g |
| Net carbs | 7.7g |
| Fiber | 1.7g |
| Sugar | 4.4g |
| Sugar alcohols | 0g |
| Protein | 1.1g |
| Fat | 0.1g |
| Sodium | 4mg |
| Potassium | 0mg |
Source: Open Food Facts (USDAHouston Food Bank). Net carbs = total carbs − fiber − sugar alcohols, computed by CarbMeNot.
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Frequently asked questions
- How many carbs are in onion?
- Onion (1 medium onion, 110g) has 10.3g of total carbs and 8.5g of net carbs. Per 100 grams: 9.4g total, 7.7g net.
- How many net carbs are in onion?
- Onion has 8.5g of net carbs per 1 medium onion (110g) — 10.3g total carbs minus 1.9g fiber.
- Is onion keto-friendly?
- Onion is borderline for keto — it works only in small portions. 1 medium onion (110g) is 8.5g net carbs (10.3g total carbs − 1.9g fiber); per 100g that is 7.7g net carbs. On a standard keto diet (20–50g net carbs per day), even one serving uses a large share of your daily carbs, so keep portions small or save it for a higher-carb day.
- How many calories are in onion?
- Onion (1 medium onion, 110g) has 44 calories; that is 40 calories per 100 grams.
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CarbMeNot provides general nutrition information, not medical advice. Values are estimates — verify before relying on them for any health decision. See our Medical Disclaimer.