Onion Calories: Exact Count Per Size & Variety (2025 Data)

A medium-sized onion (approximately 110g) contains just 44 calories, making it an excellent low-calorie ingredient for health-conscious cooking. This comprehensive guide breaks down calorie counts by onion variety, serving size, and preparation method while highlighting their nutritional benefits beyond just calorie content.

When tracking your daily calorie intake, understanding the precise nutritional value of common ingredients like onions is essential. Whether you're meal prepping, following a specific diet plan, or simply curious about what you're consuming, knowing how many calories in an onion helps you make informed dietary choices without sacrificing flavor.

Onion Calorie Counts by Variety and Size

Not all onions are created equal when it comes to calorie content. The exact number depends on the variety, size, and preparation method. Here's a detailed breakdown based on data from the USDA FoodData Central database:

Onion Type	Size	Calories	Carbohydrates	Water Content
Yellow Onion	Medium (110g)	44	10g	89%
Red Onion	Medium (110g)	42	9.8g	89%
White Onion	Medium (110g)	45	10.3g	88%
Green Onions	1 cup chopped (72g)	32	7g	87%
Shallots	1 cup chopped (117g)	72	16.8g	78%

This USDA nutritional data shows that yellow, red, and white onions have nearly identical calorie profiles, with minor variations due to slight differences in water and sugar content. Green onions contain fewer calories per serving because they're mostly water with less dense bulb structure, while shallots pack slightly more calories due to their lower water content.

Understanding Onion Nutrition Beyond Calories

While the onion calorie count is impressively low, these versatile vegetables offer significant nutritional value that extends far beyond their energy content. Onions contain valuable nutrients that contribute to overall health:

• Vitamin C: One medium onion provides about 11% of your daily recommended intake, supporting immune function and skin health
• B vitamins: Particularly B6 and folate, which aid in energy metabolism and cellular function
• Dietary fiber: Approximately 2g per medium onion, promoting digestive health and satiety
• Quercetin: A powerful antioxidant with anti-inflammatory properties, particularly abundant in red onions
• Sulfur compounds: Responsible for onions' distinctive flavor and aroma, with potential cardiovascular benefits

According to research published in the Journal of Food Science and Technology, the antioxidant capacity of onions remains relatively stable during typical cooking methods, meaning you retain significant nutritional benefits whether you consume them raw or cooked.

How Cooking Methods Affect Onion Calories

Many people wonder if how many calories in cooked onion differs significantly from raw. The answer depends on your cooking method:

• Raw onions: Maintain their natural calorie count (44 calories for medium onion)
• Sautéed onions: Add approximately 40-100 calories depending on oil quantity (1 tsp oil = 40 calories)
• Caramelized onions: Concentrate natural sugars through water evaporation, increasing calories per volume (about 70 calories per 1/2 cup)
• Roasted onions: Minimal calorie change if cooked without added fats

When tracking calories for recipes, remember that cooking reduces onion volume through water loss. One medium raw onion yields about 1/2 cup of caramelized onions but with concentrated calories from natural sugars. For precise onion calories per 100g calculations, raw onion contains 40 calories per 100g, while cooked onion can range from 45-60 calories per 100g depending on preparation.

Practical Tips for Using Onions in Calorie-Conscious Cooking

Onions' low calorie density makes them an ideal ingredient for enhancing flavor without significantly impacting your daily intake. Here's how to maximize their culinary potential while maintaining your dietary goals:

Flavor Enhancement Without Extra Calories

Use onions as a flavor foundation to reduce need for higher-calorie ingredients:

• Create rich flavor bases with onions and garlic instead of heavy creams or cheeses
• Add caramelized onions to burgers instead of mayonnaise or special sauces
• Use onion broth instead of meat-based stocks for soups and stews
• Replace some meat content in dishes with finely chopped mushrooms and onions

Portion Guidance for Different Dietary Needs

Understanding appropriate onion portions helps maintain your calorie goals:

• Weight management: 1/2 medium onion (22 calories) per meal provides flavor without excess
• Diabetes management: 1/4 medium onion contains just 11g carbs, fitting within most meal plans
• Low-FODMAP diets: Limit to 1/4 cup chopped onion (about 35g) to stay within recommended thresholds

Comparing Onion Calories to Other Common Vegetables

Understanding where onions fall in the vegetable calorie spectrum helps with meal planning. According to USDA data, onions contain fewer calories than starchy vegetables but slightly more than some watery greens:

• Onion (medium): 44 calories vs. Potato (medium): 163 calories
• Onion (medium): 44 calories vs. Carrot (medium): 25 calories
• Onion (medium): 44 calories vs. Bell Pepper (medium): 24 calories
• Onion (medium): 44 calories vs. Zucchini (medium): 33 calories

This comparison shows why onions are considered a moderate-calorie vegetable—higher than leafy greens but significantly lower than starchy vegetables. Their unique flavor profile makes them worth the slight calorie difference compared to lower-calorie options.

Storing Onions to Maintain Nutritional Value

Proper storage preserves both flavor and nutritional content. Whole onions keep best in a cool, dark, dry place with good air circulation. Avoid refrigeration for whole onions as it increases moisture and can degrade texture. Once cut, store in an airtight container in the refrigerator for up to 7 days.

Research from the Journal of Agricultural and Food Chemistry indicates that proper storage maintains onion's quercetin content for up to 3 months, while vitamin C degrades more quickly—by about 15% after one month of storage.

Conclusion: Onions as a Nutritional Powerhouse

With just 44 calories in a medium onion, these versatile vegetables offer exceptional value for health-conscious eaters. Their low calorie count combined with significant nutritional benefits makes them an excellent addition to virtually any diet. Whether you're tracking every calorie or simply looking to enhance your meals with nutritious ingredients, understanding the precise calories in onion helps you make informed choices without sacrificing flavor.

How many calories are in a small onion?

A small onion (about 80g) contains approximately 32 calories according to USDA FoodData Central. This serving provides about 7g of carbohydrates and 1.6g of fiber.

Do cooked onions have more calories than raw onions?

Cooking concentrates calories per volume as water evaporates, but doesn't add calories unless you use oil or butter. A medium raw onion (44 calories) becomes about 70 calories per 1/2 cup when caramelized due to reduced water content.

Are onions good for weight loss?

Yes, onions are excellent for weight loss diets. With only 44 calories per medium onion and 2g of fiber, they add volume and flavor to meals without significant calories. Their high water content promotes satiety while keeping calorie counts low.

Which onion variety has the fewest calories?

Green onions (scallions) have the fewest calories at 32 calories per cup chopped (72g). Among bulb onions, red onions are slightly lower in calories (42) compared to yellow (44) or white (45) onions of the same size.