How Many Calories Are in Onions?
Nearly every savoury dish in Britain starts with one, and it costs next to nothing: onions are 35 calories per 100 g raw, so a whole medium bulb is 53 kcal and the half that goes into a family dinner about 26. How many calories are in onions only becomes an interesting question at the hob, where frying nearly triples the figure to 95 per 100 g.
You'd need to walk about 7 minutes to burn the 35 calories in 100 g raw.
How long does it take to burn off onions?
100 g raw is 35 kcal. Enter your weight and the amount you ate to see how long it takes you to burn that off:
lb
| Activity | Time to burn 35 kcal |
|---|---|
| Walking, brisk | 7 min |
| Cycling, moderate | 4 min |
| Swimming, moderate | 5 min |
| Jogging | 4 min |
| Weight training, moderate | 8 min |
Times are for a 154 lb (11 st) adult at a steady pace; change the weight to see yours. The amount is set to the portion in the text (100 g); change it to what you actually ate. BodyPal works this out from your steps automatically.
On this page
- Quick facts
- The sweetest thing in the veg drawer
- Portions
- Fried, baked, boiled, pickled
- How do onions compare?
- Most popular onion products
- FAQ
Quick facts
Figures are for raw onions.
| Nutrient | Per 100 g | RI% |
|---|---|---|
| Energy | 35 kcal / 146 kJ | 2% |
| Protein | 1.0 g | 2% |
| Carbohydrates | 8.0 g | 3% |
| Fat | 0.1 g | <1% |
| Fibre | 2.2 g | – |
| Sugar | 6.2 g | 7% |
| Salt | 0.01 g | <1% |
RI = reference intake for an average adult (2,000 kcal a day).
Verified nutrition data
Numbers on this page come from CoFID, the UK government’s Composition of Foods Integrated Dataset, and from manufacturer labels where a branded product is named. Last verified August 2026. How we verify our data →
The sweetest thing in the veg drawer
Look at that sugar row again: 6.2 g per 100 g, unusually high for a vegetable, and most of the onion's carbohydrate. It is the reason onions brown, caramelise and turn sticky-sweet in a way a courgette never will. The sweetness is built in; the pan just reveals it.
It is nothing to manage, though. Sugars that arrive inside intact vegetables are not the free sugars NHS guidance asks you to limit, and the whole onion still totals 53 kcal. An 80 g portion counts towards your 5 A Day like any other vegetable.
Portions
| Portion | kcal |
|---|---|
| Half an onion in a dish | ~26 |
| 1 medium onion (~150 g) | 53 |
Most people never eat an onion as a portion; it disappears into everything else. That is worth remembering when logging home cooking: the onion in a curry for four adds about 13 kcal to your serving, and two whole onions in a soup for four still come to only 27 kcal a bowl.
Unless it came out of a frying pan swimming in oil, the onion is never the problem ingredient in a recipe. Log the fats, the meat and the starches carefully; round the onion generously and you will still be within a biscuit's width of the truth.
Fried, baked, boiled, pickled
| Onions | kcal per 100 g |
|---|---|
| Pickled, drained | 24 |
| Boiled | 25 |
| Raw | 35 |
| Baked | 43 |
| Fried in oil | 95 |
| Dried / crispy fried | 309 |
The spread tells the whole story. Boiled and baked onions stay in vegetable territory; fried onions land at 95 kcal per 100 g, nearly triple the raw figure, and CoFID's measured UK data shows the extra is the oil they cook in, not the onion. The crispy fried onions sold for burgers and salads go further still, to 309, because they are dried and fried into a different food.
Pickled onions are the opposite trap. At 24 kcal per 100 g they are the lightest version on the table, but the brine leaves them carrying 1.12 g of salt per 100 g, over a hundred times the raw onion's 0.01 g. A jar habit spends the NHS salt allowance of 6 g a day faster than it spends calories.
How do onions compare?
Onions sit at the top of this table and it still does not matter: 35 kcal per 100 g is a rounding error in any real meal, and all four vegetables are effectively interchangeable on calories.
The verdict: pick the vegetable for the dish, not the number. The only decision with calorie consequences is the cooking method, because one pan of oil outweighs every difference on this table.
Most popular onion products in the United Kingdom
Ranked by how widely each product appears among foods sold in the United Kingdom, from the BodyPal food database of over 3.3 million products. Calories are the figures printed on each label. Fresh onions are unbranded — the jars and toppers are where labels live, at opposite ends of the scale.
| Product | Calories (per 100 g) |
|---|---|
| Haywards Traditional Pickled Onions | 19 kcal |
| French's Crispy Fried Onions | 643 kcal |
Brand popularity: BodyPal food database. Nutrition: manufacturer labels.
FAQ
How many calories are in an onion?
53 calories for a medium raw onion of about 150 g. The half-onion that actually goes into most dishes is around 26 kcal, and once shared between servings it barely registers. Only frying changes this: onions cooked in oil reach 95 kcal per 100 g.
How many calories in 100g of onions?
35 kcal raw, measured in the UK CoFID dataset, with 6.2 g of natural sugar and 2.2 g of fibre. Boiled they drop to 25 kcal per 100 g and baked they sit at 43, so every plain cooking method keeps onions firmly in the vegetable price range.
How many calories in fried onions?
95 kcal per 100 g, against 35 raw, and the difference is almost entirely the cooking oil. Fried onions also concentrate slightly as water cooks off, taking sugar to 8.6 g and fibre to 3 g per 100 g. Fry them in a measured teaspoon of oil and the sums stay friendly.
How many calories in caramelised onions?
Caramelising is slow frying, so the closest measured figure is fried onions at 95 kcal per 100 g; done with minimal fat it sits nearer baked onions at 43. Long cooking drives off water and concentrates the onion's own 6.2 g of sugar, which is where the sweetness comes from, not from anything added.
How many calories in onion rings?
Onion rings are batter and deep fat more than onion, so no raw-onion figure applies. The measured relatives bracket them: fried onions at 95 kcal per 100 g and dried crispy fried onions at 309. Treat onion rings as a fried snack rather than a vegetable when logging.
How many calories in pickled onions?
24 kcal per 100 g drained, the lightest onion there is. The catch is salt: 1.12 g per 100 g from the brine, against 0.01 g in a raw onion. With the NHS daily limit at 6 g, a generous serving of pickles claims a real slice of it while contributing almost no energy.
How many calories in boiled onions?
25 kcal per 100 g, the lowest of the plain cooking methods, because the onion takes on water and adds no fat. Baked onions measure 43 kcal per 100 g. Both are lighter routes to the same sweetness that frying delivers at nearly four times the boiled price.
Are onions good for you?
They are a low-calorie vegetable: 35 kcal per 100 g with 2.2 g of fibre and almost no fat or salt, and an 80 g portion counts towards your NHS 5 A Day. Their sugars are the kind that come inside whole vegetables, not the free sugars the NHS asks you to cap.
Similar foods
- Carrot — 27 kcal per medium carrot
- Cauliflower — 23 kcal per 80 g portion
- Broccoli — 22 kcal per 80 g portion
- Cabbage — 14 kcal per boiled portion
- Pepper — 42 kcal per red pepper
- Cucumber — 11 kcal per 5 cm piece
Chop it, snap it, done
Photograph the finished plate and BodyPal logs the onions along with the oil that cooked them.
