Onions may be beloved for their flavor, but when you're tracking fat intake, knowing exactly how much fat is hiding in your serving matters. This calculator converts any onion portion into total fat grams, with values based on the onion form you choose — from raw slices and sautéed bits to onion powder and crispy fried onions.
Simply enter your portion weight, select the onion type, and the tool does the rest. You'll receive total fat, fat per 100 grams, calories contributed by fat, and a daily-value reference based on a 2,000-calorie diet. The built-in quick portions make logging common servings effortless.
Whether you're meal-prepping, counting macros, or following a low-fat eating plan, this calculator keeps your onion numbers straight — no more guessing, just accurate nutrition data.
🧅 Onion Fat Per 100g
Find out how much fat is in any onion serving — total fat, calories from fat, and daily value.
How to Use This Tool
Enter the amount of onion you plan to eat in the weight field and choose the unit — grams, ounces, pounds, or kilograms. If you are using a food scale, grams give the most accurate result. The quick-portrait buttons below the onion-type list load common portions like one medium onion or one cup of chopped onion instantly, so you don't have to weigh anything for rough estimates.
Next, choose the form of onion that matches what is actually on your plate. Raw onion is nearly fat-free, but sautéed, fried, and powdered forms have very different fat values. The calculator stores a fat-per-100-gram value for each type, so the only thing you need to enter is the portion weight.
Fat Content by Onion Form
The dropdown values come from USDA FoodData Central and practical cooking estimates. The table below summarizes the reference numbers.
| Onion form | Fat per 100 g | Notes |
|---|---|---|
| Raw yellow or white onion | 0.10 g | Effectively fat-free |
| Red onion, raw | 0.10 g | Same fat, more anthocyanins |
| Green onion / scallion | 0.20 g | Bulb and leaves included |
| Boiled / cooked, no fat added | 0.14 g | Water changes concentration slightly |
| Sautéed in oil | 6.00 g | Depends on how much oil clings |
| Dehydrated onion flakes | 0.32 g | Concentrated but still low fat |
| Onion powder | 0.35 g | Use a food scale for exact grams |
| French-fried onions | 32.00 g | Breaded and fried, high fat |
These are useful starting values. Branded seasonings, added butter, or restaurant preparations can change the numbers.
How the Calculation Works
The formula behind the calculator is simple:
If your weight is not already in grams, the calculator converts it first: 1 oz = 28.3495 g, 1 lb = 453.592 g, 1 kg = 1,000 g. Then it multiplies by the fat factor for the selected onion type.
For example, a 200 g portion of raw onion gives (200 ÷ 100) × 0.10 = 0.20 g of fat. The same 200 g portion of sautéed onion gives (200 ÷ 100) × 6.00 = 12.0 g of fat. The difference is mostly the oil, which is why selecting the right form matters.
Besides total fat, the tool reports calories from fat (9 kcal per gram) and a daily value percentage based on 78 g of total fat — the Daily Value used for a 2,000-calorie diet.
Worked Examples
Three realistic situations show how the numbers play out.
Example 1: Salad with raw red onion
You add 50 g of raw red onion. Total fat = (50 ÷ 100) × 0.10 = 0.05 g. Calories from fat ≈ 0.5 kcal. The onion barely moves your fat total.
Example 2: Sautéed onions on a sandwich
You cook 120 g of sliced onion in a little oil. Using the sautéed value, total fat = (120 ÷ 100) × 6.00 = 7.2 g, about 65 kcal from fat. The oil you add to the pan can make this higher.
Example 3: Green bean casserole topping
A 30 g serving of French-fried onions contains (30 ÷ 100) × 32.00 = 9.6 g fat, or 86 kcal from fat. A small crunchy topping can still be significant.
Tips for Accurate Tracking
- Weigh raw, choose raw. For salads, sandwiches, and wraps, weigh the raw onion before adding it to your meal.
- Log cooking oil separately. The sautéed value is a reasonable estimate, but the oil you pour into the pan can add several grams of fat. Track that oil as its own line item for precision.
- Watch portion sizes. A medium onion weighs about 110 g, a cup of chopped raw onion about 160 g. The quick buttons are handy, but a food scale is more accurate.
- Use kitchen conversions when needed. For general weight conversion help, check the lb-to-g conversion tool.
Frequently Asked Questions
Do onions count as fat-free?
Not technically. Raw onions contain about 0.10 g fat per 100 g. In practice, a typical serving rounds down to 0 g on many nutrition labels, but precise macro tracking counts it.
Does boiling remove or add fat?
Boiling doesn't add fat, and it doesn't remove the tiny amount that's naturally present. The slight difference between raw and cooked values per 100 g comes from water loss and measurement variance.
Why are sautéed onions so much higher in fat?
They absorb and get coated by oil during cooking. Depending on how generously you oil the pan, sautéed onions can range from 2 to 8 g fat per 100 g. Our 6.00 g value reflects a typical pan-sautéed preparation.
Are caramelized onions similar to sautéed onions?
Caramelized onions are cooked slowly, often with butter or oil, so their fat content can be similar to or higher than sautéed onions. If you use butter, track it separately. For another allium with its own nutrition profile, see the garlic nutrition calculator.