Carbs in Onion
Keto-friendlyHow many carbs are in onion?
Onion has 7.7g net carbs per 100g — 9.4g total carbs minus 1.7g fiber — plus 1.1g protein, 0.1g fat, and 40 calories. 1 medium onion (110g) works out to about 8.5g net carbs and 44 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 per 100 g, sourced from Open Food Facts; net carbs are computed by CarbMeNot.
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Last updated June 10, 2026 · Reviewed by Jordan Lee, Nutrition Editor
Values per 100 g.
Is onion keto-friendly?
Yes, onion can fit a keto diet in moderate portions. It has 7.7g net carbs per 100g (9.4g total carbs − 1.7g fiber). A typical serving — 1 medium onion (110g) — is about 8.5g net carbs. On a standard keto diet (20–50g net carbs per day), that leaves plenty of room for other vegetables and meals.
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 has 40 calories per 100g. 1 medium onion (110g) has about 44 calories. That's alongside 1.1g protein, 0.1g fat, and 7.7g net carbs per 100g.
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 has 9.4g of total carbs and 7.7g of net carbs per 100 grams.
- How many net carbs are in onion?
- Onion has 7.7g of net carbs per 100 grams (total carbs 9.4g minus 1.7g fiber).
- Is onion keto-friendly?
- Yes, onion can fit a keto diet in moderate portions. It has 7.7g net carbs per 100g (9.4g total carbs − 1.7g fiber). A typical serving — 1 medium onion (110g) — is about 8.5g net carbs. On a standard keto diet (20–50g net carbs per day), that leaves plenty of room for other vegetables and meals.
- How many calories are in onion?
- Onion has 40 calories per 100 grams.
- How many carbs are in 1 medium onion?
- 1 medium onion (110g) has about 8.5g net carbs, 10.3g total carbs, and 44 calories.
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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.