About the Nutrition Label Portion Calculator
Nutrition Facts labels list values for one serving, but few people eat exactly one serving. This calculator scales every number on the label to your real portion — enter the serving size in grams and the label values, then either the weight you ate or the number of servings — and it shows calories, fat, saturated fat, carbohydrate, fiber, sugars, protein and sodium for that amount.
It is handy for logging food when you weigh portions on a kitchen scale, for comparing two products with different serving sizes (calories per 100 g puts them on equal footing), and for checking how a “single-serve” bag that actually holds 2.5 servings adds up.
Percent Daily Values use the current FDA Daily Values for adults and children 4 and over, which assume a 2,000-calorie diet. The calculation is simple proportional scaling, so it is exactly as accurate as the label you enter.
With the default inputs, the calories in your portion is 210 kcal. Change any value above to recalculate instantly.
How to use the nutrition label portion calculator
- 1Enter the serving size in grams and the calories from the label.
- 2Copy the fat, carbohydrate, sugar, protein and sodium values per serving.
- 3Choose whether you will enter the weight you ate or the number of servings.
- 4Weigh your portion (or count servings) and enter it.
- 5Read the scaled calories and nutrients, and the %DV chart for your portion.
Formula and method
Nutrition Facts values scale in direct proportion to the amount of food. If the label serving is 30 g and you eat 45 g, you ate 1.5 servings, so every nutrient is multiplied by 1.5. If you enter servings directly, that number is the multiplier.
Calories per gram is calories per serving divided by the serving weight, and calories per 100 g multiplies that by 100 — useful for comparing products with different serving sizes. Percent Daily Values use the FDA Daily Values for adults and children 4 and over: 78 g total fat, 20 g saturated fat, 275 g carbohydrate, 28 g fiber, 50 g added sugars, 50 g protein and 2,300 mg sodium.
- serving size
- Gram weight of one serving printed on the label
- servings eaten
- Multiplier applied to every label value
- Daily Value
- FDA reference amount used for %DV
Worked examples
45 g of a cereal with a 30 g serving
45 g ÷ 30 g = 1.5 servings, so 140 kcal becomes 210 kcal, 7 g fat becomes 10.5 g and 160 mg sodium becomes 240 mg. The cereal has 140 ÷ 30 × 100 ≈ 467 kcal per 100 g.
Two servings of granola
Eating two 55 g servings doubles everything: 460 kcal, 16 g fat, 20 g added sugars (40% of the 50 g Daily Value) and 320 mg sodium.
100 g of chips with a 28 g serving
100 g ÷ 28 g ≈ 3.57 servings. That is about 571 kcal, 36 g of fat and 607 mg of sodium — roughly a quarter of the 2,300 mg Daily Value.
Frequently asked questions
How do I calculate calories for my portion size?+
Divide the grams you ate by the serving size in grams, then multiply the label calories by that number. For example, 45 g of a food with 140 kcal per 30 g serving is 140 × 1.5 = 210 kcal.
How do I find calories per 100 g?+
Divide calories per serving by the serving weight in grams and multiply by 100. A 28 g serving with 160 kcal works out to about 571 kcal per 100 g.
Is the serving size how much I should eat?+
No. US serving sizes reflect amounts people typically eat, not recommendations. They are a reference point for comparing foods, which is why scaling to your real portion matters.
Why weigh food instead of using cups?+
Volume measures vary with how food is packed or poured, especially for cereal, rice, nuts and shredded cheese. Weighing in grams with a kitchen scale matches the label’s gram serving size much more accurately.
What does %DV mean?+
Percent Daily Value shows how much of a day’s reference amount a portion provides, based on a 2,000-calorie diet. The FDA considers 5% DV or less low and 20% DV or more high.