Calories in Onion

44kcal per 1 medium onion (110 g)

40 kcal per 100 g · about 2% of a 2,000-kcal day

Onions add flavor to nearly any dish for around 44 calories per whole onion — the oil they are cooked in is what adds up.

Onion nutrition facts

NutrientPer 100 gPer 1 medium onion
Calories40 kcal44 kcal
Protein1.1 g1.2 g
Carbs9.3 g10.2 g
Fat0.1 g0.1 g
Fiber1.7 g1.9 g
Sugar4.2 g4.6 g

Where the calories come from

Onion calories by serving size

ServingCaloriesProteinCarbsFat
1 oz (28 g)11 kcal0.3 g2.6 g0 g
50 g20 kcal0.6 g4.7 g0.1 g
100 g40 kcal1.1 g9.3 g0.1 g
1 medium onion (110 g)44 kcal1.2 g10.2 g0.1 g
200 g80 kcal2.2 g18.6 g0.2 g
250 g100 kcal2.8 g23.3 g0.3 g

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Values based on USDA FoodData Central reference entries. Actual nutrition varies with variety, preparation, and portion. © 2026 NibbleCal.