Red onion calories come to 87 for one onion (197 g) and 44 per 100 g. What stands out is how lean the rest of the label is: 89% of those calories come from carbs, a whole onion carries 4.3 g of fiber, and sodium sits at just 2 mg.
87kcal
1 onion · 197 g, raw
8%protein
1.9 gProtein
20 gCarbs
0.2 gFat
How to burn off 87 kcal
—Walking, brisk
—Jogging
—Cycling, moderate
—Swimming
Skip the math. BodyPal counts these calories from your steps and workouts automatically.
Nutrition facts
Raw · per 197 g
Calories
87 kcal
Protein
1.9 g
Carbohydrate
19.6 g
Fat
0.2 g
Sodium
2 mg
Potassium
388 mg
Iron
0.5 mg
Source: USDA FoodData Central
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Verified nutrition data
Numbers on this page come from USDA FoodData Central, the U.S. Department of Agriculture’s food composition database, and from manufacturer labels where a branded product is named. Last verified September 2026. How we verify our data →
Red onion: calories, protein and sodium by serving
Percent of daily value uses the FDA reference of 2,000 kcal a day.
Serving
kcal
Protein
Carbs
Fat
Sodium
% DV kcal
1 onion (197 g)
87
1.9 g
19.6 g
0.2 g
2 mg
4%
3 oz portion (85 g)
37
0.8 g
8.4 g
0.1 g
1 mg
2%
100 g
44
0.9 g
9.9 g
0.1 g
1 mg
2%
3 × 1 onion (197 g)
260
5.6 g
6 mg
5 × 1 onion (197 g)
433
9.3 g
10 mg
A whole red onion is an 87-calorie ingredient
One red onion of 197 g comes to 87 calories, about 4% of a daily value of 2000. That is the number to log if a recipe calls for a whole onion. Most people never eat a full onion in one sitting, though. A 3 oz portion (85 g), which is closer to a generous handful of slices on a burger or salad, comes to 37 calories.
The total only moves in a meaningful way when onions become a base ingredient. Two onions (394 g) add 173 calories to a pot, three onions (591 g) add 260, and five onions (985 g) add 433. That last figure is a batch of caramelized onions or a large soup, and it gets split across many servings.
So the practical rule is simple. Raw red onion as a topping barely registers in a day of eating. If you cook down several onions for a recipe, log the full weight once and divide by the portions you serve, rather than guessing per bowl.
Carbs supply 89% of the calories
Per 100 g, red onion has 9.9 g of carbohydrate, 0.9 g of protein and 0.1 g of fat. Run that through the calorie split and carbs account for 89% of the energy, protein for 8% and fat for 2%. Nearly every calorie here is carbohydrate, which is typical for a bulb vegetable.
Part of that carbohydrate is fiber: 2.2 g per 100 g, or 4.3 g in a whole onion. The rest is the natural sugar and starch that give red onion its sweetness once it softens in a pan. Across a full onion you get 19.6 g of carbs, which matters more for someone counting carbs closely than for someone counting calories.
Protein is not a reason to eat onions. A whole one gives 1.9 g, about 4% of the daily value, and fat is a rounding error at 0.2 g. Treat red onion as a flavor and volume ingredient, and get protein from whatever it sits on.
Fiber is the row worth reading, not sodium
Raw red onion is close to sodium-free. One onion has 2 mg, which rounds to 0% of the daily value, and 100 g has 1 mg. If you watch sodium, fresh onion is one of the easiest ways to add sharp flavor to a dish without moving that row at all.
Fiber is the more useful number. A whole onion provides 4.3 g against a daily value of 28 g, and even a 3 oz portion adds 1.9 g. Potassium shows up too, at 197 mg per 100 g, though that is a modest share of the 4700 mg daily value.
One caution: these figures are for raw red onion. Jarred products such as Jeff's Garden Pickled Red Onions or Mezzetta Sweet & Tangy Pickled Red Onions are a different food, made with brine and often sweetened. If you use them, check the jar label for sodium and sugar rather than borrowing the raw numbers on this page.
Red onion adds flavor for very few calories
Red onion earns its place on salads, tacos, grain bowls, burgers and salsas because it brings color and bite for 37 calories per 3 oz. It pairs well with lean proteins like chicken, beans or fish, and with tomatoes, cucumbers and avocado. The onion itself will rarely be the calorie problem on the plate.
Preparation is where the count changes. Sliced raw, the numbers above hold. Sauteed or caramelized, the onion soaks up whatever oil or butter goes into the pan, and that fat often adds more calories than the onion. Log the cooking fat as its own line if you want an honest total.
Pre-cut options such as Created Fresh Diced Red Onion or store-brand bags from ShopRite and Ahold are the same raw vegetable, just trimmed. Weigh what you actually use, or snap a photo of your plate and let BodyPal log it for you.
How does red onion compare?
Here is how red onion stacks up against white, yellow and green onion, per 100 g and per usual serving.
Verdict: If you want the fewest calories per 100 g, green onion at 32 and white onion at 35 edge out red onion at 44, with yellow onion at 38 in between. The gap is small enough that you should pick red onion for its color and sharper raw bite, not avoid it to save calories.
Most popular red onion brands in the United States
5Created Fresh Diced Red Onion1/2 cup · 85 g41 kcal
Pickled red onions sit in a sweetened brine, so they read higher than plain raw onion, while the fresh whole-onion labels are the same raw state as the number above. Source: manufacturer labels / USDA FoodData Central.
Red onion FAQs
How many calories are in one red onion?
A whole raw red onion weighing 197 g has about 87 calories. Per 100 g, red onion has 44 calories.
Is red onion good for weight loss?
Red onion is 44 calories per 100 g with 2.2 g fiber and only 0.1 g fat, so a 3 oz portion (85 g) adds 37 calories.
Red onion vs plain onion: which has more calories?
Plain onion averages 40 calories per 100 g, so red onion at 44 calories per 100 g is 4 calories higher.
How many carbs are in red onion?
Red onion has 9.9 g carbs per 100 g, of which 2.2 g is fiber. A whole 197 g onion has 19.6 g carbs and 4.3 g fiber.
How many calories are in 100 g of red onion?
Red onion has 44 calories per 100 g. That weight also gives 9.9 g of carbs, 2.2 g of fiber, 0.9 g of protein and 0.1 g of fat, so carbs make up 89% of the calories.
How many calories are in 3 oz of red onion?
A 3 oz portion (85 g) of raw red onion has 37 calories. It also carries 8.4 g of carbs, 1.9 g of fiber and 0.8 g of protein, which is about 2% of the daily value for calories.
How much fiber is in a red onion?
One red onion (197 g) has 4.3 g of fiber, against a daily value of 28 g. Per 100 g it comes to 2.2 g, and a 3 oz portion gives 1.9 g.
Is red onion high in sodium?
No. A whole raw red onion has only 2 mg of sodium, which is 0% of the daily value, and 100 g has 1 mg. Pickled red onions are a different product, so check their label.
How much protein is in a red onion?
One red onion has 1.9 g of protein, about 4% of the daily value. Protein supplies only 8% of its calories, so red onion works as a flavor ingredient rather than a protein source.
