Onions are easy to overlook in a protein count, but they contribute measurable amounts of protein to soups, stir-fries, salads, and roasted dishes. This calculator tells you how many grams of protein are in the onions you plan to use, whether you measure them in grams, ounces, chopped cups, or whole onions. Choose the variety that matches your recipe — yellow, white, red, sweet, green onion, or leek — and the tool does the rest.
Protein values come from standard USDA food-composition data and are adjusted for typical onion weights and varieties. The result is an estimate, not a lab measurement, because natural crops vary slightly in moisture and nutrient content. Use it for meal planning, macro tracking, or just to learn more about a humble vegetable that adds flavor and a small protein boost to almost any savory dish.
🧅 Onion Protein Calculator
Estimate protein in any amount of onions, from a single slice to a full cup.
How to Use This Calculator
Start by choosing the onion variety closest to what you are cooking with. Yellow and white onions are the default because they are the most common, but the dropdown also includes red onions, sweet/Vidalia onions, green onions (scallions), leeks, and boiled onion. Next, enter the amount you plan to use. You can type a number in grams or ounces, or choose “cups, chopped,” “medium onion,” or “large onion” from the unit menu. The quick-add buttons below the input are handy shortcuts: ½ cup, 1 medium, 3 oz, and 100 g.
Press Calculate Protein to see the estimated protein in grams, along with the converted weight and the protein density used for the calculation. Use the Reset button to clear the form, or Copy Result to copy the main figure to your clipboard for a food log or meal-planning note.
How Onion Protein Is Estimated
The calculator uses standard USDA food-composition values for the protein content of each onion type per 100 g of edible portion. The equation is straightforward:
When you choose a non-gram unit, the calculator first converts it to grams using typical portion weights: 1 cup of chopped raw onion ≈ 160 g, 1 medium onion ≈ 110 g, and 1 large onion ≈ 150 g. These are average weights, so whole-onion estimates are less precise than gram or cup measurements. For a more exact figure, weigh the onion on a kitchen scale and enter grams directly.
Protein Content by Onion Type
The table below shows the approximate protein values used by this calculator. Values are for raw onion unless noted, per 100 g of edible flesh.
| Onion type | Protein per 100 g |
|---|---|
| Yellow / white onion (raw) | 1.1 g |
| Red onion (raw) | 1.0 g |
| Sweet / Vidalia onion (raw) | 0.9 g |
| Green onion / scallion (raw) | 1.8 g |
| Leek (raw) | 1.5 g |
| Onion, boiled / cooked | 1.4 g |
Because onions are roughly 89% water, their protein density is low. A whole medium yellow onion contains only about 1.2 g of protein. Still, onions are rarely eaten alone; when added to stews, omelets, grain bowls, and sauces, their protein counts as part of the total meal.
Worked Examples
Example 1: 1 cup of chopped yellow onion
1 cup = 160 g. Protein = (160 ÷ 100) × 1.1 = 1.76 g.
Example 2: 3 oz of green onion
3 oz = 85.0 g. Protein = (85.0 ÷ 100) × 1.8 = 1.53 g.
Example 3: ½ cup of red onion
½ cup = 80 g. Protein = (80 ÷ 100) × 1.0 = 0.80 g.
Tips for Better Accuracy
Weigh raw onion before cooking when possible. Moisture loss during cooking increases protein per 100 g by weight, even though the total protein in the onion stays essentially the same. If you cook a large batch, weigh the raw ingredients and divide by the number of servings rather than relying on cooked-volume estimates.
For leafy green onions, use the white and green parts together, as the protein value of 1.8 g per 100 g represents the whole scallion. Leeks should be trimmed of the dark green tops and root ends before weighing.
Onion protein is incomplete on its own, but it complements other foods. Pair onion-heavy dishes with legumes, eggs, dairy, poultry, or whole grains if you are aiming for a complete amino-acid profile.
Frequently Asked Questions
Is onion protein worth counting?
For strict macro tracking, yes. A cup of chopped onion provides 1.5–1.8 g of protein, depending on variety. That may look small on its own, but onions are often used in large quantities in soups, stir-fries, and roasted vegetable trays. Over a week, those additions can amount to several grams of protein.
Do cooked onions have more protein?
Per 100 g, cooked onions usually show a slightly higher protein value because water evaporates during cooking, concentrating the remaining nutrients. The absolute amount of protein in the onion does not change, only the water content. This calculator includes a boiled-onion option for recipes that list cooked onion by weight.
Which onion has the most protein?
Among common types, green onions and scallions have the highest protein density at about 1.8 g per 100 g, followed by leeks at 1.5 g. Yellow, white, red, and sweet onions are all close to 0.9–1.1 g per 100 g, so variety makes only a small difference for most recipes.
Do I need to log onion protein?
If you track protein closely to hit a daily target, include all sources for accuracy. A medium onion is only about 1.2 g, but a recipe with three onions can contribute several grams across multiple servings. For casual eaters, the difference is minor; for athletes and bodybuilders on strict targets, it is worth including.
Reference values are consistent with data published by the USDA FoodData Central. If you are planning out a full day of meals, you may also find the chicken nutrition calculator useful for comparing a higher-protein ingredient, or the fiber goal calculator when you want to balance the rest of your plate.