Nutrition label calculator: per 100 g to your portion

A food label tells you what is in 100 g of the food, or in one serving, but you rarely eat exactly that. This calculator scales every figure on the label to the amount you actually eat, gives the energy in both kcal and kJ, converts between salt and sodium, and checks whether the label's energy adds up from its own nutrients.

Per 100 g, per portion or per serving

In the EU, the nutrition declaration has to give the energy and nutrients per 100 g or per 100 ml (Regulation (EU) No 1169/2011, Article 32). A label may add a per-portion column, but the per-100 g figures are always there, which makes them the easiest to use. A US Nutrition Facts label gives everything per serving, with the serving size in grams or millilitres after the household measure.

Choose the column you are copying from, type the figures, and enter your amount: in grams or millilitres, or in servings when you copied a per-serving column.

kJ and kcal

One kilocalorie is 4.184 kilojoules. EU labels print kJ first, then kcal. They work out each figure from the nutrients with their own factors and round each one separately, so the two numbers rarely match the exact conversion. The quick converter under the calculator does the plain conversion: 1000 kJ is 239 kcal.

Salt and sodium

EU labels give salt, and the regulation defines it as sodium × 2.5 (Annex I, point 11). US labels give sodium in milligrams. Tick the sodium box if your label is one of those, and the calculator gives you both.

The energy check

The regulation fixes the energy each nutrient counts for (Annex XIV): 9 kcal per gram of fat, 4 for carbohydrate and protein, 2 for fibre, 2.4 for polyols and 7 for alcohol. When you enter the fat, carbohydrate and protein, the calculator adds them up and compares the total with the label's own energy.

A small gap is normal. The European Commission's guidance lets a label round figures of 10 g and more to the nearest gram, and smaller ones to 0.1 g, and the check allows for exactly that. A bigger gap usually means a nutrient the label doesn't list, such as fibre, polyols or alcohol, or a figure copied from the wrong column.

A worked example

A granola label gives, per 100 g: 1885 kJ and 450 kcal, 17 g fat of which 3.5 g saturates, 60 g carbohydrate of which 18 g sugars, 7 g fibre, 10 g protein and 0.3 g salt. These are illustrative figures, not a real product.

For a 40 g bowl, every figure is multiplied by 40 ÷ 100 = 0.4: 180 kcal (754 kJ), 6.8 g fat, 1.4 g saturates, 24 g carbohydrate, 7.2 g sugars, 2.8 g fibre, 4 g protein and 0.12 g salt, which is 48 mg of sodium. The label's nutrients add up to 447 kcal per 100 g against the 450 it prints, a gap its rounding explains.

Reference intakes

EU labels may show each figure as a percentage of a reference intake: 8400 kJ or 2000 kcal, 70 g fat, 20 g saturates, 260 g carbohydrate, 90 g sugars, 50 g protein and 6 g salt (Annex XIII, Part B). The calculator can show the same percentages for your amount. They are one fixed reference for an average adult, the same on every label, not a personal target.

What it can't tell you

It trusts the figures you type, and the label's figures are rounded averages. EU guidance accepts a margin between the declared value and what a laboratory finds: for a protein figure of 12 g, for example, the Commission's guidance works through a tolerance of 20%. The calculator can show that a label doesn't add up; it can't say which figure is wrong.

How do I convert kJ to kcal?

Divide by 4.184. A label's 1885 kJ is 450.5 kcal, and the label prints 450 because it rounds each figure on its own. To go the other way, multiply kcal by 4.184.

Does carbohydrate include fibre?

On an EU label, no: carbohydrate and fibre are separate lines, and fibre counts 2 kcal per gram on its own. On a US label, Total carbohydrate includes the dietary fibre listed under it. Tick "Carbohydrate includes fibre" for a US label, so the energy check doesn't count the fibre twice.

Why does my label's energy not match its nutrients?

Rounding explains a gap of a few kcal. A larger one usually comes from something the label doesn't list separately, such as polyols in sugar-free sweets or alcohol, or from a US label, which may use any of several methods the US rules permit for working out calories (21 CFR 101.9).

Sources

• Regulation (EU) No 1169/2011 on the provision of food information to consumers: Article 32, Annex I point 11 (salt), Annex XIII Part B (reference intakes) and Annex XIV (energy factors).
• European Commission, Guidance document for competent authorities on tolerances for nutrient values declared on a label, December 2012: the rounding guidelines in Table 4.
• US Food and Drug Administration, How to understand and use the Nutrition Facts label.
• 21 CFR 101.9, paragraph (c)(1)(i): the ways a US label may work out calories.

For dishes in a restaurant, the menu calorie calculator does the same arithmetic with the weight a menu prints. For drinks, which rarely carry a label, use the drink calorie calculator.