A worked example
A 40 g serving of biscuits whose label says 480 kcal, 22 g fat and 28 g sugars per 100 g comes to 192 kcal, 8.8 g fat and 11 g sugars. That’s 10% of an adult’s reference intake for energy.
How the calculation works
Every figure on the label is scaled by the same factor: what you ate divided by the amount the label describes. Eat 40 g of something labelled per 100 g and every figure is multiplied by 0.4, energy and salt alike.
If the pack prints energy in kilojoules, the calculator divides by 4.184 for kilocalories and shows both. Use the energy printed on the label rather than adding up the macros yourself, because the label figures are rounded and the sum drifts.
What “% RI” means
RI is the reference intake EU labels use for an average adult: 2000 kcal, 70 g fat, 20 g saturates, 260 g carbohydrate, 90 g sugars, 50 g protein and 6 g salt a day, set out in Regulation 1169/2011. It’s a yardstick for comparing foods, and your own needs can be quite different. Fibre has no RI on the label.
Salt and sodium
EU labels give salt, and the regulation defines it as sodium × 2.5. So 1 g of salt is 400 mg of sodium, which is how the sodium line is worked out. If you’re comparing with a US label, that one lists sodium in milligrams directly.
The low, medium and high colours
The coloured tags are the UK’s front-of-pack traffic lights, the red, amber and green you see on British packs. They rate the food per 100 g, so a portion can’t make a salty crisp look healthy: high starts at a quarter of an adult’s reference intake in 100 g. A portion bigger than 100 g is high as well when it alone holds more than 30% of the reference intake. The thresholds are set in government guidance and apply to food; drinks have their own, lower thresholds.
| Nutrient | Low | Medium | High |
|---|---|---|---|
| Fat | ≤ 3 g | 3 g – 17.5 g | > 17.5 g |
| Saturates | ≤ 1.5 g | 1.5 g – 5 g | > 5 g |
| Sugars | ≤ 5 g | 5 g – 22.5 g | > 22.5 g |
| Salt | ≤ 0.3 g | 0.3 g – 1.5 g | > 1.5 g |
Questions people ask
Should I use the per 100 g or the per serving column?
Either works, as long as the “figures are for” box matches it. Per 100 g is usually easier, because the manufacturer’s idea of a serving is rarely what ends up in the bowl.
Why doesn’t protein × 4 + carbs × 4 + fat × 9 match the energy?
Labels round each figure, fibre adds about 2 kcal per gram, and some foods contain alcohol or polyols with energy values of their own. Trust the printed energy.
Does it matter whether I weigh before or after cooking?
The label describes the food as sold, which is usually raw or dry. Weigh it the same way. For cooked food use the raw to cooked calculator.