How Many Calories Are There In An Onion? | Quick Facts Guide

What Changes The Calories In An Onion

Raw onion is light. Most of the bulb is water with a little carbohydrate and a touch of protein. The base number you can use is ~40 calories per 100 grams, or ~44 calories for a typical medium bulb. Differences come from bulb size, variety, and what goes in the pan with it.

Size has the biggest swing. A small onion around 70 grams lands near 28 calories. A large bulb near 150 grams lands near 60 calories. Red, yellow, and white sit in the same range. The shifts are modest in day-to-day cooking.

Onion Calories By Size, Type, And Common Dishes

Item	Typical Portion	Calories
Raw yellow onion	1 medium (110 g)	~44 kcal
Raw red onion	1 medium (110 g)	~44 kcal
Raw white onion	100 g	~35 kcal
Green onion (scallion)	1 medium (15 g)	~5 kcal
Roasted onion wedges	1 cup roasted (~160 g)	~64–90 kcal
Caramelized onions	1/2 cup cooked	~80–150 kcal+
Sautéed onions in oil	1 cup cooked	~130 kcal
Onion rings, breaded & fried	100 g	~330–480 kcal

Cooking Styles And Real-World Portions

Heat drives off moisture and can deepen flavor. The vegetable itself stays mild on calories. The big swing comes from fat. A single tablespoon of olive oil adds 119 calories per tablespoon to the pan. That extra energy attaches to every sweet strand of onion.

Roasting uses less oil than pan work if you keep the coat thin. Caramelizing calls for a longer time. The longer time invites more sips of oil and that stacks up fast. If you prefer a softer profile, let onions sweat in a covered pan with a small splash of water, then finish with a light brush of oil.

Crumbing and frying is a different food. Batter brings flour and fat. Deep oil adds more. That is why onion rings can land in the mid-hundreds per serving.

How Many Calories Are There In An Onion By Size

You can get close with a simple rule. Start from 40 calories per 100 grams. Then scale by the weight of the bulb. Kitchen scales help, but a quick look works too. Small is about the size of a tennis ball cut in half, medium is a tennis ball, and large leans bigger than a tennis ball.

Quick Size Guide

Small (~70 g): about 28 calories. Medium (~110 g): about 44 calories. Large (~150 g): about 60 calories. These figures fit raw bulbs. Cooking moves water and can change the serving mass on the plate.

Do Types Of Onions Change The Count

Color does not move the needle much. White onions can read a touch lower per 100 grams than yellow or red, but the split is modest. Sweet onions taste sweeter because the bite is gentler, not because they hold a big sugar load. Scallions are even lighter per stalk since each piece weighs far less.

Raw, Roasted, Or Caramelized

Raw slices keep the number tight and clean. Roasting adds flavor through heat. Caramelizing builds a deep brown profile. The vegetable sugars darken and bring a richer taste. Most of the extra calories come from added fat. Use a spritz bottle or brush to gain control.

Tips For Lower-Oil Cooking

• Start with a nonstick pan and a splash of water to soften.
• Add a teaspoon of oil near the end for sheen.
• Finish with a pinch of salt and a bright hit like lemon or vinegar.

Onion Nutrition Beyond Calories

Per 100 grams you get single-digit grams of carbohydrate, a gram of protein, and a little fiber. There is vitamin C and a modest amount of potassium. The water load keeps energy density low. As a cooking base, that helps balance dishes that carry denser items like meat or cheese.

Use onions to add bulk and taste without sending portions off the rails. A cup of roasted wedges fits neatly beside fish or chicken. A spoon of caramelized strands can lift a burger. Just count the oil that went into the pan.

Raw Onion Nutrition Per 100 Grams

Nutrient	Amount	Notes
Calories	~40 kcal	low energy density
Carbohydrates	~9–10 g	mostly natural sugars
Fiber	~1.7–2 g	adds fullness
Protein	~1 g	minor amount
Vitamin C	~7–10 mg	about 8–12% DV
Potassium	~140–150 mg	helps balance sodium

Everyday Counting Examples

Sandwich: two rings of raw onion weigh about 10–15 grams. That is roughly 4–6 calories. The slice of cheese and the spread do the heavy lifting. Stir-fry: half a medium onion in a quick pan sear adds about 20 calories before fat. Add one teaspoon of oil and you tack on 40 more.

Soup base: one large onion sweated in a pot contributes near 60 calories. If you gloss with a tablespoon of butter, add about 102. Tray bake: two medium onions roasted with chicken thighs bring under 100 calories from the bulbs. The marinade and skin set the bigger number.

Buying, Storage, And Prep That Help With Portions

Pick firm bulbs with dry skins. Avoid soft spots. Store in a cool, dry, ventilated spot, not the fridge drawer. Keep them away from potatoes to slow sprouting. Cut onions last to match what you plan to eat. Leftovers in a sealed container keep fine in the fridge for a few days.

For quick weeknights, slice two or three medium bulbs at once. Cook them dry in the oven on a lined tray until they slump and sweeten. Divide into small containers. Each portion is easy to log and easy to use.

Smart Ways To Use Onion Calories

Think of onions as flavor carriers. Use them to bring volume and aroma while you steer the fats. Brush, don’t pour. Measure once, then cook by feel. If you want a full plan for daily targets, try our daily calorie needs guide.