How much fiber is in an onion?
Onions have 1.9 grams of fiber in 1 medium onion (110 grams), according to USDA FoodData Central. That is 7% of the Daily Value, below the 10% the FDA requires before a label can call a food a good source of fiber. Per 100 grams, onions have 1.7 grams of fiber.
1.9gof fiber in 1 medium onion
8% of a 25 gram day
Fiber in onions by serving size
| Serving | Weight | Fiber |
|---|---|---|
| 1 slice, thin | 9g | 0.2g |
| 1 tbsp chopped | 10g | 0.2g |
| 1 slice, medium (1/8" thick) | 14g | 0.2g |
| 1 slice, large (1/4" thick) | 38g | 0.6g |
| 10 rings | 60g | 1g |
| 1 small | 70g | 1.2g |
| 1 medium (2-1/2" dia) | 110g | 1.9g |
| 1 cup, sliced | 115g | 2g |
| 1 large | 150g | 2.6g |
| 1 cup, chopped | 160g | 2.7g |
| 100 grams | 100g | 1.7g |
How onions compare with other vegetables
Onions rank 7 of 13 vegetables in this library, by fiber in one serving.
- Broccoli2.4g
- Brussels sprouts2g
- Onion1.9g
- Carrots1.7g
- Tomato1.5g
Each bar is one serving: broccoli, 1 cup, chopped; Brussels sprouts, 1/2 cup, cooked; onion, 1 medium onion; carrot, 1 medium carrot; tomato, 1 medium tomato.
You rarely eat a whole one
A medium onion has 1.9 grams of fiber, but most meals use a few slices. Count a quarter of an onion as about 0.5 grams.
It adds up in a pot
One onion cooked into a pot with a cup of lentils is 17.5 grams of fiber for the pot.
More fiber alongside onions
- Chickpeas: 12.5 grams in 1 cup, cooked
- Quinoa: 5.2 grams in 1 cup, cooked
- Lentils: 15.6 grams in 1 cup, cooked
Not sure what your daily number should be? The fiber calculator works it out from your age and sex.
Questions about fiber in onions
- How much fiber is in an onion?
- Onions have 1.9 grams of fiber in 1 medium onion, which weighs 110 grams. The number comes from USDA FoodData Central.
- Are onions high in fiber?
- One serving, 1 medium onion, has 1.9 grams. That is 7% of the Daily Value, below the 10% the FDA requires before a label can call a food a good source of fiber. Onions rank 7 of 13 vegetables in this library by fiber per serving.
- How much fiber is in 100 grams of onions?
- 1.7 grams of fiber per 100 grams. The largest size USDA lists, 1 cup, chopped, weighs 160 grams and has 2.7 grams of fiber.
- How many onions would it take to reach 25 grams of fiber?
- About 13.2, at 1.9 grams each. Most people reach 25 grams by mixing several foods across the day.
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Source: USDA FoodData Central, Onions, raw, retrieved October 8, 2026. Label terms follow the FDA's 28 gram Daily Value for fiber.