Onion
40 kcal per 100g
Onion has 40 kcal per 100 g, and 1 medium (110 g) comes to about 44 kcal, with 1.2 g protein, 10 g carbs and 0.1 g fat.
Kairo logs Onion from a photo: the app estimates the portion on the plate and fills in calories and macros from reference data, no typing needed.
Your portion
Type the grams or the calorie budget you have left.
- 1.1 g
- Protein
- 9.3 g
- Carbs
- 0.1 g
- Fat
100 g ≈ 2 % of a 2,000 kcal reference intake. Work out your own daily need
Nutrition Facts
Serving size: 100g
Compare with: Asparagus · Beetroot · Bell Pepper (red)
Health Info
Onions are low in calories and a notable source of quercetin, an antioxidant flavonoid, plus prebiotic fibers that feed gut bacteria. Their sulfur compounds (released when chopped) are being studied for cardiovascular benefits.
Macros per 100g
Values per 100 g are based on recognised nutrition reference data. Last reviewed: June 2026. View sources
Track Onion in Kairo
Just photograph it. Kairo's AI reads the portion and the nutrition. Three seconds later the calories and macros are in your log, no typing.
Get Kairo on the App StoreFrequently Asked Questions
- How many calories are in Onion?
- Onion has 40 kcal per 100 g. A typical 110 g serving contains about 44 kcal.
- How much protein is in Onion?
- Onion provides 1.1 g of protein per 100 g.
- How many carbs are in Onion?
- Onion contains 9.3 g of carbohydrates per 100 g, of which 4.2 g is sugar.
- How much fat is in Onion?
- Onion contains 0.1 g of fat per 100 g. It also provides 1.7 g of fiber per 100 g.
- Is Onion good for weight loss?
- With only 40 kcal per 100 g, Onion is low in calories and fits easily into a weight-loss diet.
- Can I log Onion in Kairo from a photo?
- Yes, photograph the plate and Kairo estimates the portion of Onion, then logs calories and macros from reference data. If the portion looks off, you can adjust the grams and the numbers update.