How to Read Nutrition Labels: Grams, Ounces, Calories and Serving Sizes
A food label is a dense little table of measurements: grams, milligrams, ounces, fluid ounces, calories, kilojoules and percentages, often in two systems at once. Most people glance at the calorie number and move on, but a little unit literacy reveals much more — and helps you compare products fairly.
This guide uses the US Nutrition Facts panel as its main example and notes where European and UK labels differ.
Serving size: the number everything else depends on
Every nutrient figure on a US label is given per serving, so the serving size is the first thing to read. It appears in a familiar household measure (such as 2/3 cup or 1 bar) followed by the metric equivalent in grams or millilitres. Two products can look similar per serving while having very different serving sizes, which makes direct comparison misleading.
For labelling purposes, the US Food and Drug Administration uses rounded household equivalents: 1 teaspoon = 5 mL, 1 tablespoon = 15 mL, 1 cup = 240 mL, 1 fluid ounce = 30 mL and 1 ounce = 28 g. Note that the labelling cup of 240 mL is slightly larger than the US customary cup of about 236.6 mL used in cooking.
Labels also state the number of servings per container. A bottle of juice listing 110 calories per serving with 2.5 servings per container contains 275 calories in total.
Net weight versus fluid volume
The front of a US package shows the net quantity, usually in both customary and metric units, for example “NET WT 16 OZ (1 LB) 454 g”. For solid foods “oz” means weight (avoirdupois ounces). For drinks the label uses fluid ounces, a measure of volume, and adds “FL” — “12 FL OZ (355 mL)” on a can of soda.
The two ounces are not interchangeable. Eight fluid ounces of water happens to weigh close to eight ounces, but eight fluid ounces of honey weighs nearly 12 ounces, and eight fluid ounces of cereal flakes weighs only one or two. If you need to compare value between products, the price per 100 grams or per 100 millilitres is the most reliable figure.
Calories, kilocalories and kilojoules
The “Calories” on a food label are actually kilocalories — the energy needed to raise one kilogram of water by one degree Celsius. In nutrition the capitalised Calorie and the kilocalorie (kcal) are the same thing.
European, UK and Australian labels also give energy in kilojoules (kJ), the SI unit. One kilocalorie equals 4.184 kilojoules, so a 250 kcal snack contains about 1,046 kJ. If a label shows only kilojoules, divide by roughly 4.2 to get Calories.
Energy comes from the macronutrients at approximately fixed rates: about 4 kcal per gram of carbohydrate, 4 kcal per gram of protein, 9 kcal per gram of fat and 7 kcal per gram of alcohol. You can sanity-check a label using these factors.
| Nutrient | Energy per gram | Example |
|---|---|---|
| Carbohydrate | ~4 kcal (17 kJ) | 30 g carbs ≈ 120 kcal |
| Protein | ~4 kcal (17 kJ) | 20 g protein ≈ 80 kcal |
| Fat | ~9 kcal (37 kJ) | 10 g fat ≈ 90 kcal |
| Alcohol | ~7 kcal (29 kJ) | 14 g alcohol ≈ 98 kcal |
What % Daily Value means
The % Daily Value (%DV) column shows how much of a recommended daily amount one serving provides, based on a reference diet of 2,000 Calories a day. A common rule of thumb is that 5% DV or less is low and 20% DV or more is high. For nutrients you want to limit, such as sodium and saturated fat, aim for lower percentages; for fibre, vitamin D, calcium, iron and potassium, higher is generally better.
European labels use a similar concept called Reference Intakes, and are required to show nutrition per 100 g or 100 mL, which makes comparing products easier than the US per-serving approach.
Sodium versus salt
US labels list sodium in milligrams; the Daily Value is 2,300 mg. UK and EU labels list salt in grams instead. Salt (sodium chloride) is about 40% sodium by weight, so to convert, multiply sodium by 2.5 to get salt: 600 mg of sodium is equivalent to about 1.5 g of salt. Going the other way, divide salt by 2.5.
Rounding rules that hide small amounts
Labels are allowed to round. In the US, a serving with fewer than 5 Calories can be labelled as 0, and a serving containing less than 0.5 g of fat, sugar or trans fat can be listed as 0 g. If you eat several servings of a product labelled “0 g trans fat”, the small amounts can add up. Checking the ingredients list for “partially hydrogenated” oils is a more reliable test.
Sugar figures are easier to picture if you convert them: a level teaspoon of granulated sugar weighs about 4 grams, so a drink with 40 g of sugar contains the equivalent of roughly ten teaspoons.