How Many Calories Are In One Onion? | Quick Facts Guide

Onion Calories By Size And Variety

Onions are low in calories. Raw onions average about 40 calories per 100 grams. A medium onion lands near 44 calories because it weighs around 110 grams. Red, white, yellow, and sweet onions all sit in the same ballpark for energy per gram.

To keep your math honest, match the weight to the bulb in your hand. Store onions lose water over time, so two medium onions can differ by a few grams. Trim loss from the root and papery skin also nudges the final number.

Type Or Size	Typical Weight	Calories
Small yellow, raw	80–90 g	32–36 kcal
Medium yellow, raw	~110 g	~44 kcal
Large yellow, raw	150–175 g	60–70 kcal
Medium red, raw	~110 g	~46 kcal
Medium white, raw	~110 g	~42 kcal
1 cup chopped, raw	~160 g	~64 kcal

Those figures line up with federal references. The USDA SNAP-Ed onion page lists 44 calories for one medium onion at 110 grams, while MyFoodData pegs one cup chopped at 64 calories from 160 grams.

Fiber sits in a friendly range for a low-calorie vegetable. One cup chopped has roughly 2.7 grams. That helps meals feel balanced without heavy energy load.

If you track fiber along with energy targets, dialing in recommended fiber intake can steady portions and keep meals satisfying.

How Cooking Changes The Calories

Raw onion calories don’t shift until fat enters the pan. Heat alone drives off water and softens texture. The count per bite seems higher after cooking only because each forkful weighs less.

Once oil joins the party, the math changes. A single teaspoon of oil adds about 40 calories. If a skillet of onions soaks up one teaspoon per 100 grams, the dish roughly doubles in energy compared with raw.

Close Variant Keyword: Calories In One Onion By Preparation

When readers search for calories in one onion, they usually mean a whole bulb in a tortilla, salad, omelet, or burger. A quick estimator helps. Start with 40 calories per 100 grams raw. Weigh your portion after trimming. Then add any cooking fat.

Quick Estimator Steps

1. Weigh the onion or the chopped portion you’ll eat.
2. Multiply grams × 0.40 to get raw calories.
3. Add 40 calories for each teaspoon of oil that clings to that portion.

Real-World Examples

Half a medium onion in a skillet, cooked with one teaspoon of oil that mostly stays in the pan, lands near 25 raw calories plus a small share of the oil. A full medium onion slowly caramelized in a tablespoon of butter or oil can cross 150 calories.

Nutrition Beyond Calories

Onions bring aroma and crunch with a light energy tag. One cup chopped has about 15 grams of carbs and 2.7 grams of fiber. Vitamin C shows up in modest amounts. Minerals like potassium appear in small doses.

Macros At A Glance

• Carbs: ~9–10 g per 100 g
• Protein: ~1 g per 100 g
• Fat: ~0.1 g per 100 g
• Water: ~89% by weight

Why Portion And Method Matter

The same onion can fit into many goals. Raw rings keep calories lowest. Light sauté builds sweetness and texture. Heavy caramelization with added fat boosts flavor and energy. Pick the style that fits your dish and day.

Smart Ways To Use Onion Calories

Keep Sandwiches Punchy

Thin raw slices add bite with minimal energy. Stack them under tomato to protect bread from moisture. A few rings weigh little yet change the whole bite.

Boost Volume In Salads

Use paper-thin half-moons tossed with lemon and a pinch of salt. That cuts sharpness and blends into greens. You get crunch without a calorie surge.

Build Flavor In The Pan

Measure oil before it hits the skillet. Start with one teaspoon, add a splash of water if sticking starts, and let onions steam-sauté. You keep browning while holding calories in check.

Picking The Right Onion For The Job

Flavor differs more than calories across varieties. Yellow onions are all-rounders. Sweet types like Vidalia or Walla Walla run a touch lower in acid and taste mild. Red onions shine raw. White onions stay crisp in salsa and tacos.

Swaps That Keep Numbers Steady

• Swap red for yellow in salads without changing calories much.
• Use sweet onions for milder raw bite at the same energy per gram.
• Try shallots when you want gentle onion notes in dressings.

Storing And Prepping Without Losing Track

Keep whole bulbs in a cool, dry spot with airflow. Cut onions keep in the fridge for a few days in a sealed container. Weigh after trimming if you want tight tracking. Dry outer layers and root ends don’t count toward your serving.

Common Pitfalls

• Eyeballing oil into the pan, which hides calories.
• Assuming cooked weight matches raw weight.
• Using “medium” as a fixed size; weights vary by batch.

Cooked Onion Calories At A Glance

Here’s a late-stage check for cooked portions. These numbers blend reference data with simple fat-math so you can budget quickly during meal prep.

Method (Per 100 g)	What It Means	Calories
Raw, sliced	No fat added	~40 kcal
Grilled, dry	On a hot pan, no oil	~40–45 kcal
Sautéed in 1 tsp oil	Oil absorbed per 100 g	~80 kcal
Sautéed in 1 Tbsp oil	Oil absorbed per 100 g	~160 kcal
Yellow, sautéed	USDA reference data	~130 kcal

That last line mirrors the USDA-based entry for sautéed yellow onions at roughly 132 calories per 100 grams. If your pan uses less oil, your number lands lower. If you caramelize low and slow with more fat, it climbs.

Sources You Can Trust

Federal references keep numbers consistent. The MyFoodData onion entry compiles USDA data for common measures, and the USDA SNAP-Ed page lists one medium onion at 44 calories.

Cook with intention, measure, enjoy the flavor payoff daily.

Want more structure for your day? Try our daily calorie needs guide to set a clean target before you cook.