How much protein is in raw onions?

Raw onions has 1.1 g of protein per 100 g and 1.8 g per 1 cup, chopped (160 g). That is 2.8 g of protein per 100 kcal — essentially not a protein source.

Where do these calorie figures come from?

USDA FoodData Central record 170000, “Onions, raw” (SR Legacy, FDC SR Legacy 2018-04 + FNDDS 2024-10-31). Energy is USDA nutrient 1008 (Energy, kcal); protein, fat and carbohydrate are read from the same record. USDA data is in the public domain, and the FDC ID above links straight to it.

All foods

Everyday vegetablesUSDA SR LegacyFDC 170000

Calories in raw onions

USDA FoodData Central record for “Onions, raw” — per 100 g, per every USDA serving size, and next to the other everyday vegetables rows.

The short answer

Raw onions: 40 kcal per 100 g. 1 cup, chopped (160 g) is 64 kcal with 1.8 g of protein. Source: USDA FoodData Central record 170000, "Onions, raw".

Per 100 g

Nutrient	Per 100 g	Share of energy
Energy	40 kcal	100%
Protein	1.1 g	10%
Fat	0.1 g	2%
Carbohydrate	9.3 g	88%

Raw onions is 40 kcal per 100 g in USDA FoodData Central (SR Legacy). Of that energy, about 10% comes from protein, 2% from fat and 88% from carbohydrate. That works out to 2.8 g of protein per 100 kcal — essentially not a protein source.

Per serving

The serving sizes USDA lists for this record, priced from the per-100 g figures above. Nothing here is rounded to a “portion” — the gram weight next to each label is what the calories are computed from.

Serving	Weight	Calories	Protein	Fat	Carbs
100 g	100 g	40	1.1 g	0.1 g	9.3 g
1 cup, chopped	160 g	64	1.8 g	0.2 g	14.9 g
1 cup, sliced	115 g	46	1.3 g	0.1 g	10.7 g
1 tbsp chopped	10 g	4	0.1 g	0 g	0.9 g
1 large	150 g	60	1.7 g	0.2 g	14 g
1 slice, large (1/4" thick)	38 g	15	0.4 g	0 g	3.5 g
1 medium (2-1/2" dia)	110 g	44	1.2 g	0.1 g	10.2 g
1 slice, medium (1/8" thick)	14 g	6	0.2 g	0 g	1.3 g
1 small	70 g	28	0.8 g	0.1 g	6.5 g

Compared with other everyday vegetables

Food	kcal / 100 g	Protein / 100 g	Per serving
Raw carrots	41	0.9 g	52 kcal · 1 cup chopped
Raw tomatoes	18	0.9 g	32 kcal · 1 cup, chopped or sliced
Raw cucumber	15	0.7 g	45 kcal · 1 cucumber (8-1/4")
Raw onions	40	1.1 g	64 kcal · 1 cup, chopped
Raw red bell pepper	26	1 g	39 kcal · 1 cup, chopped
Raw white mushrooms	22	3.1 g	15 kcal · 1 cup, pieces or slices
Sweet corn	86	3.3 g	123 kcal · 1 ear, large (7-3/4" to 9" long) yields
Green peas	81	5.4 g	117 kcal · 1 cup

Other tables in vegetables and vegetable products

The same numbers for the foods this one usually shares a plate — or a shopping list — with.

Questions about raw onions

How many calories are in raw onions?: Raw onions: 40 kcal per 100 g. 1 cup, chopped (160 g) is 64 kcal with 1.8 g of protein. Source: USDA FoodData Central record 170000, "Onions, raw".
How much protein is in raw onions?: Raw onions has 1.1 g of protein per 100 g and 1.8 g per 1 cup, chopped (160 g). That is 2.8 g of protein per 100 kcal — essentially not a protein source.
Where do these calorie figures come from?: USDA FoodData Central record 170000, “Onions, raw” (SR Legacy, FDC SR Legacy 2018-04 + FNDDS 2024-10-31). Energy is USDA nutrient 1008 (Energy, kcal); protein, fat and carbohydrate are read from the same record. USDA data is in the public domain, and the FDC ID above links straight to it.

How calorie.one logs it

Type “raw onions” into calorie.one and the app matches this exact record — “Onions, raw” — estimates the grams, and shows the line with its USDA label. You correct the amount; the per-100 g figure is never guessed. That split between recognition and arithmetic is the whole methodology. For the numbers in context, read How to track mixed meals accurately with AI.