Vegetables

Red onion calories and nutrition

½ cup of chopped raw onion (80 g) has 32 calories, with 0.9 g of protein, 7.5 g of carbs and 0.1 g of fat. That is 40 calories per 100 g.

Raw onion, generic USDA variety estimate. Data: USDA FoodData Central, “Onions, raw”. SR Legacy has no red-onion-specific entry. This page uses USDA’s generic raw onion data as an estimate for red onion; it is not a measured red cultivar analysis.

½ cup, chopped · 80 g

32 calories

Protein: 0.9 g10% of calories · 2% DV
Carbs: 7.5 g88% of calories · 3% DV
Fat: 0.1 g2% of calories · 0% DV

Fiber: 1.4 g
Sugars: 3.4 g
Saturated fat: 0.0 g
Sodium: 3.2 mg

Red onion nutrition facts: the variety estimate

This USDA serving (80 g) has 32 calories, 0.9 g protein, 7.5 g carbs and 0.1 g fat. The figures apply to raw onion, generic USDA variety estimate; use the serving table to match your portion. Sources ↓

Calories in red onion by serving

Serving	Calories	Protein	Carbs	Fat
½ cup, chopped80 g	32	0.9 g	7.5 g	0.1 g
1 cup, chopped160 g	64	1.8 g	15 g	0.2 g
1 medium slice, ⅛-inch thick14 g	6	0.2 g	1.3 g	0.0 g
100 g100 g	40	1.1 g	9.3 g	0.1 g

Serving weights are USDA’s household measures for this food.

Red onion nutrition facts

Per 100 g, 40 calories: 10% from protein, 88% from carbs and 2% from fat.

Nutrient	Per 100 g	Per serving½ cup, chopped · 80 g	% Daily Value
Calories	40	32	–
Total fat	0.1 g	0.1 g	0%
Saturated fat	0.0 g	0.0 g	0%
Cholesterol	0 mg	0 mg	0%
Sodium	4.0 mg	3.2 mg	0%
Total carbohydrate	9.3 g	7.5 g	3%
Dietary fiber	1.7 g	1.4 g	5%
Total sugars	4.2 g	3.4 g	–
Protein	1.1 g	0.9 g	2%
Vitamin D	0 µg	0 µg	0%
Calcium	23 mg	18 mg	1%
Iron	0.2 mg	0.2 mg	1%
Potassium	146 mg	117 mg	2%
Vitamin A	0 µg	0 µg	0%
Vitamin C	7.4 mg	5.9 mg	7%

% Daily Value is per serving (½ cup, chopped), using the FDA’s Daily Values. Calorie shares use 4 calories per gram of protein and carbs and 9 per gram of fat.

How long to walk it off

Walking at 3 mph, a 150-lb adult burns about 3.2 calories a minute on top of what they would burn at rest. So ½ cup of chopped raw onion (32 calories) takes about 10 minutes of walking, roughly 1,100 steps.

Work it out for your weight and pace →

Related foods to explore

Roma tomato11 calories in a USDA reference plum tomato18 per 100 g
Green bell pepper24 calories in a medium raw green bell pepper20 per 100 g
Mini cucumber4 calories in 1 oz of raw cucumber with peel15 per 100 g
Cos lettuce8 calories in a cup of shredded raw romaine lettuce17 per 100 g

All foods →

Red onion questions

How much protein is in ½ cup of chopped raw onion?

½ cup of chopped raw onion (80 g) has 0.9 g of protein, 2% of the 50 g Daily Value. That is 1.1 g per 100 g.

How many calories are in red onion?

½ cup of chopped raw onion (80 g) has 32 calories: 0.1 g fat, 7.5 g carbs (1.4 g of it fiber) and 0.9 g protein.

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Sources

U.S. Department of Agriculture, FoodData Central: Onions, raw (FDC ID 170000, SR Legacy, published 2019-04-01).
U.S. Food and Drug Administration. Daily Value on the Nutrition and Supplement Facts Labels.
Walking time: the method of our walking calorie calculator (2024 Adult Compendium of Physical Activities; CADENCE-Adults for steps).

Prepared by the KaloCam team · Updated October 21, 2026