How Many Calories in an Onion? Exact Count & Nutrition Facts

A medium raw onion (110g) contains exactly 44 calories. This complete guide breaks down calorie counts by onion variety, cooking methods, and practical usage tips for healthy meal planning.

Onion Nutrition: Your Quick Reference Guide

Onions are kitchen staples that add flavor without significant calories. Whether you're tracking macros or building balanced meals, knowing precise nutritional values helps. Let's explore the facts backed by USDA data.

Calorie Counts by Onion Type

Calorie content varies slightly by variety and size. Here's the breakdown per 100g (standard measurement) and per medium onion:

Onion Type	Calories per 100g	Calories per Medium Onion (110g)	Carbohydrates
Yellow Onion	40	44	9.3g
Red Onion	40	44	9.5g
White Onion	42	46	10.0g
Scallions (Green Onions)	32	18 (per 55g bunch)	7.0g

Source: USDA FoodData Central (2023 update) - fdc.nal.usda.gov

How Cooking Affects Calorie Density

Raw onions maintain their natural calorie profile, but cooking changes water content and concentration:

• Caramelizing: Reduces water content by 60%, concentrating calories. 100g cooked becomes ~100 calories but shrinks to 40g volume
• Grilling/Roasting: Minimal calorie change per serving, though volume decreases by 30-40%
• Frying: Adds significant calories from oil absorption (up to 150 calories per tbsp oil used)

For accurate tracking, weigh onions before cooking. A medium raw onion (110g) yields about 65g cooked.

Why Onions Are Nutrition Powerhouses

Beyond low calories, onions deliver impressive benefits:

• Fiber boost: 1.7g per medium onion (7% daily value) supports digestion
• Vitamin C: 11% of daily needs in red onions enhances immunity
• Quercetin: Potent antioxidant in yellow onions reduces inflammation
• Zero fat and negligible sodium make them ideal for heart-healthy diets

Practical Usage Tips for Healthy Cooking

Maximize flavor without excess calories:

• Raw applications: Use in salsas, salads, and sandwiches for crunch and 44 calories per medium onion
• Low-calorie sautéing: Cook with 1 tsp oil instead of 1 tbsp (saves 120 calories)
• Flavor layering: Sauté onions first to build depth in soups/stews using just 20 calories per serving
• Portion control: A 1/4 cup diced onion adds big flavor for only 11 calories

Common Questions Answered

How many calories in a small onion?

A small onion (80g) contains approximately 32 calories. This equals about 1/2 cup chopped onions.

Do cooked onions have more calories than raw?

Per 100g, cooked onions have higher calorie density due to water loss, but the total calories in the original onion remain unchanged. A medium raw onion (44 calories) becomes more concentrated when cooked but doesn't gain calories unless oil is added.

Are onions good for weight loss?

Yes. With only 44 calories per medium onion and high fiber content, they add volume and flavor to meals while promoting fullness. Their low energy density makes them ideal for weight management diets.

Which onion has the fewest calories?

Green onions (scallions) have the lowest calorie count at 32 calories per 100g. A full bunch (55g) contains just 18 calories, making them excellent for garnishing without significant calorie impact.