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 13 of 22 vegetables in this library, by fiber in one serving.
- Brussels sprouts2g
- Zucchini2g
- Onion1.9g
- Beets1.7g
- Carrots1.7g
Each bar is one serving: Brussels sprouts, 1/2 cup, cooked; zucchini, 1 medium zucchini; onion, 1 medium onion; beets, 1/2 cup, sliced, cooked; carrot, 1 medium carrot.
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.
Fiber in cooked onions
USDA FoodData Central lists boiled onions (record 170001) at 1.4 grams of fiber per 100 grams, against 1.7 for raw. A medium boiled onion weighs 94 grams and has 1.3 grams, where a raw one has 1.9. A cup of chopped boiled onion has 2.9 grams, a little more than the 2.7 in a cup of raw, because cooked onion packs down and the cup weighs 210 grams instead of 160.
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. For a longer list to shop from, see 50 high-fiber foods ranked by fiber.
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 13 of 22 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.