Onions are a staple in kitchens worldwide, prized for their flavor and versatility. But if you're tracking carbohydrates for keto, low-carb, or diabetic meal planning, knowing exactly how many carbs are in 100 grams of onion is essential. This calculator gives you the precise net carbs, total carbs, fiber, and sugar content for common onion varieties — yellow, red, white, sweet, and green onion.
Whether you're a home cook, a nutrition student, or someone managing blood sugar, this tool helps you make informed choices. Simply select the onion type and enter the weight in grams, and the calculator instantly breaks down the macronutrient profile. Use it to compare varieties, adjust portion sizes, or log your daily intake with confidence.
🧅 Onion Carbs Per 100g
How to Use This Tool
Select the onion variety from the dropdown — yellow, red, white, sweet, or green onion (scallion). Enter the weight in grams (default is 100 g). Click Calculate to see the total carbs, fiber, net carbs, and sugar for that portion. Use the preset buttons (50 g, 100 g, 150 g, 200 g) for quick common servings. The Reset button clears the results and returns to default values.
How It Works
The calculator uses standard USDA nutrition data per 100 grams for each onion type. It multiplies the per-100g values by your entered weight divided by 100. Net carbs are calculated as total carbs minus fiber, which is the figure most relevant for low-carb and keto diets. Sugar is reported separately as part of total carbs.
Formula: Nutrient (g) = (Nutrient per 100g) × (Weight in g / 100)
Example Calculations
Example 1: 150 g of red onion. Total carbs = 9.17 × 1.5 = 13.76 g. Fiber = 1.7 × 1.5 = 2.55 g. Net carbs = 13.76 − 2.55 = 11.21 g. Sugar = 4.73 × 1.5 = 7.10 g.
Example 2: 50 g of green onion. Total carbs = 7.34 × 0.5 = 3.67 g. Fiber = 2.6 × 0.5 = 1.3 g. Net carbs = 3.67 − 1.3 = 2.37 g. Sugar = 2.33 × 0.5 = 1.17 g.
Example 3: 200 g of sweet onion. Total carbs = 7.55 × 2 = 15.10 g. Fiber = 1.1 × 2 = 2.20 g. Net carbs = 15.10 − 2.20 = 12.90 g. Sugar = 5.02 × 2 = 10.04 g.
Example 4: 75 g of white onion. Total carbs = 9.34 × 0.75 = 7.01 g. Fiber = 1.7 × 0.75 = 1.28 g. Net carbs = 7.01 − 1.28 = 5.73 g. Sugar = 4.24 × 0.75 = 3.18 g.
Tips & Best Practices
- Weigh onions raw before cooking for the most accurate carb count, as water loss during cooking concentrates nutrients.
- For keto, net carbs under 20–50 g per day is typical — a 100 g serving of yellow onion provides about 7.6 g net carbs, so plan accordingly.
- Sweet onions have slightly lower total carbs but higher sugar, so net carbs are similar to yellow onions.
- Green onions (scallions) are the lowest in carbs and highest in fiber, making them a great choice for low-carb diets.
- If you are using a food scale, remember that one medium yellow onion (about 150 g) yields roughly 14 g total carbs and 11.5 g net carbs.
Frequently Asked Questions
Are onions keto-friendly? Yes, in moderation. A 100 g serving of yellow onion has about 7.6 g net carbs, which fits into a standard keto macro budget if you account for other carbs.
Do cooked onions have more carbs? Cooking does not change the carb content significantly, but it reduces water content, so the same weight of cooked onion will have more carbs per gram. Always measure raw for consistency.
What about onion powder or dried onions? Dried onions are much more concentrated — about 80 g carbs per 100 g. Use a separate calculator for dried forms.
Where does the data come from? The values are sourced from the USDA FoodData Central database, which is the standard reference for nutrition facts in the United States.
Can I use this for meal prep? Absolutely. This tool is designed to help you quickly estimate carbs for any onion portion, making it easier to log meals or plan recipes. For example, if a recipe calls for 1 cup of chopped yellow onion (about 160 g), you can enter 160 g to get the exact carb count.
Reference Data
| Onion Type | Total Carbs (g/100g) | Fiber (g/100g) | Net Carbs (g/100g) | Sugar (g/100g) |
|---|---|---|---|---|
| Yellow | 9.34 | 1.7 | 7.64 | 4.24 |
| Red | 9.17 | 1.7 | 7.47 | 4.73 |
| White | 9.34 | 1.7 | 7.64 | 4.24 |
| Sweet | 7.55 | 1.1 | 6.45 | 5.02 |
| Green (Scallion) | 7.34 | 2.6 | 4.74 | 2.33 |
This table summarizes the per-100g values used in the calculator. Net carbs are calculated as total carbs minus fiber. All data is from the USDA FoodData Central database.