Nutrition Label Calculator for Your Portion
This nutrition label calculator turns the values per 100 g or per serving on a food label into the amounts in your real portion. Copy the label, enter what you ate, and see the results.
Calculate your portion
1. The label values are for
Using a “per serving” column? Enter the serving size printed next to it, for example 30 g.
2. How much you ate
3. Values on the label (leave blank to skip)
| Nutrient | Label | Your portion |
|---|
“Calculated” values were converted from another line on the label (salt ↔ sodium, kcal ↔ kJ). Results carry any rounding already on the label.
How the nutrition label calculator works
Nutrition labels give values for a fixed reference amount, usually 100 g, 100 mL or one stated serving. Your portion is almost never exactly that, so every value has to be multiplied by the same factor:
your value = label value × amount eaten ÷ label amount
Units are converted exactly before dividing, so a label per 100 g and a portion weighed in ounces still works (2 oz = 56.7 g). If you choose to count label servings instead, each value is simply multiplied by the number of servings.
Two conversions fill in lines that your label may not show:
salt (g) = sodium (mg) × 2.5 ÷ 1000, the factor set in EU labelling law. US labels show sodium; UK and EU labels show salt.kJ = kcal × 4.184. If a label prints only one energy figure, the other is calculated.
Worked example: a bowl of cereal
A cereal label gives these values per 100 g. A 45 g bowl is 0.45 of that amount:
| Nutrient | Per 100 g | 45 g bowl |
|---|---|---|
| Energy | 380 kcal | 171 kcal |
| Protein | 10 g | 4.5 g |
| Sugars | 12 g | 5.4 g |
| Salt | 0.6 g | 0.27 g |
Milk added to the bowl has its own label. Calculate it separately and add the two together.
Getting an accurate answer
- Weigh your portion once. Weighing removes the guesswork, especially for cereal, nuts, rice and cooking oil.
- Check “as sold” versus “as prepared”. Some labels describe the dry product, others the cooked or made-up food. Use the column that matches what you weighed.
- Remember labels are rounded. Regulations allow rounding and natural variation, so treat results as the label’s figures, not a laboratory measurement.
For practical ways to use what you learn from labels, see our guides to foods rich in fiber, the high blood pressure diet (where salt matters most) and the type 2 diabetes diet. Whichever you choose, the nutrition label calculator gives you the numbers for the portion on your plate.
Sources for these figures
- EU Regulation 1169/2011 on food information to consumers: salt = sodium × 2.5.
- NIST Guide to the SI, Appendix B.9: 1 kilocalorie (thermochemical, as used in nutrition) = 4.184 kJ.
- US FDA: how to understand and use the Nutrition Facts label.
- NHS: how to read food labels.
Frequently Asked Questions
Divide the amount you ate by 100 and multiply by the label value. A cereal with 380 kcal per 100 g, eaten as a 45 g bowl, gives 380 × 45 ÷ 100 = 171 kcal. Weighing your portion once on a kitchen scale makes this far more accurate than guessing.
Salt is sodium chloride. Labels in the UK and EU show salt; US labels show sodium in milligrams. Salt = sodium × 2.5, so 400 mg of sodium is 1 g of salt. Enter whichever your label shows and the calculator works out the other.
Both measure energy. 1 kcal (what most people call a “calorie”) is 4.184 kJ. Many labels print both; if yours shows only one, the calculator converts it.
Manufacturers round label values, and the per-serving column is sometimes calculated from unrounded data. Small differences of a few calories or a tenth of a gram are normal and are not an error in your calculation.
Yes. If the label gives values per 100 mL, choose millilitres and enter how much you drank in mL, cups or fluid ounces. Weight and volume cannot be mixed, because that would need the drink’s density.