What Does The UK Call Calories? Understanding kcal and kJ on Food Labels

December 3, 2025 •

2 min read

According to the NHS, an average man in the UK needs around 2,500kcals a day to maintain a healthy weight, while an average woman needs 2,000kcals. This essential energy information, displayed prominently on food packaging, can be confusing due to the variety of units used.

Quick Summary

The UK refers to nutritional energy colloquially as 'calories' but officially lists it as both kilocalories (kcal) and kilojoules (kJ) on food labels due to regulatory standards.

Key Points

Kilocalorie (kcal) is the correct term: On UK food labels, the term 'kcal' represents the nutritional energy value.
'Calories' is a colloquialism: In daily conversation, people in the UK typically say 'calories' but are referring to kilocalories (kcal).
Kilojoules (kJ) are also listed: UK law requires energy to be shown in both kcal and kJ on pre-packaged foods.
Conversion is simple: 1 kilocalorie is equal to approximately 4.2 kilojoules.
Context is key: The 'small calorie' from science is 1/1000th of a 'food Calorie' (or kilocalorie), which is why the prefixes matter.
UK labels provide dual units: This accommodates both consumer familiarity with 'calories' and the internationally recognized SI unit, the kilojoule.
Traffic light system: Many UK food items feature a front-of-pack 'traffic light' label for quick nutritional reference, including kcal.

The Difference Between 'Calorie' and 'Kilocalorie'

Understanding the terms 'calorie' and 'kilocalorie' is key. Scientifically, a small 'calorie' (lowercase 'c') is the energy needed to raise the temperature of one gram of water by one degree Celsius. This unit is too small for measuring food energy.

The Colloquial UK Usage

In the UK, when people talk about 'calories' in food, they are actually referring to kilocalories (kcal). One kilocalorie equals 1,000 scientific calories. The term 'calorie' is commonly used as a shorthand. This is similar to the US, although US labels often use 'Cal' (capital C) to represent kilocalories.

What to Expect on UK Food Labels

UK food labels must display nutritional information, including energy content in both kilojoules (kJ) and kilocalories (kcal). This requirement stems from former EU standards and bridges the gap between the familiar kcal and the international standard unit, the kilojoule.

Mandatory Display: Both kJ and kcal figures must be clearly shown, usually per 100g or 100ml.
Traffic Light System: Many UK products also feature a front-of-pack traffic light label, which includes the kcal value as a quick reference.
Portion Size: While the 100g/ml value is standard, information per serving is also often provided, though portion sizes can vary by manufacturer.

The Conversion: From Kilocalories to Kilojoules

Since both units are present, you can convert between them. The conversion factor is approximately: 1 kilocalorie (kcal) ≈ 4.2 kilojoules (kJ).

For example, 200 kcal is roughly 840 kJ. To convert kJ to kcal, you divide by 4.2. Understanding this conversion is useful if you have a preference for one unit.

Why Two Different Units? A Historical Context

The dual labeling of kcal and kJ in the UK combines traditional practice with international standards. Kilocalories have long been the unit for dietary energy, while kilojoules are the metric system's standard energy unit. Displaying both ensures clarity for consumers familiar with 'calories' and aligns with scientific measurements.

UK vs. US Food Labelling: A Comparison


Feature	UK Food Labelling	US Food Labelling
Energy Units	Both kilojoules (kJ) and kilocalories (kcal) are mandatory.	"Calories" is the standard term, which refers to kilocalories.
Portion Size	Required per 100g/ml for comparison. Portion-based data is voluntary.	All nutrition data is based on a serving size determined by the manufacturer.
Standard Display	Typically uses a 'traffic light' colour-coding system on the front of packs.	Does not use a traffic light system, relies on a standard nutrition facts panel.
Salt/Sodium	Lists salt content in grams.	Lists sodium content in milligrams.

Conclusion

In the UK, 'calories' typically refers to kilocalories (kcal) in a nutritional context. While labels use 'kcal' and also include kilojoules (kJ), for practical dietary purposes, 'kcal' can be read as 'calories'. The dual system provides both a familiar figure and a scientific standard. Understanding the difference simplifies reading UK food labels for health and diet management. More information on UK nutrition requirements can be found at the Food Standards Agency.

Frequently Asked Questions

In a nutritional context, yes. The term 'calorie' is used colloquially in the UK to refer to a kilocalorie, or 'kcal'. Food labels display 'kcal' for accuracy, but the public uses the terms interchangeably.

UK food law, based on former EU regulations, mandates that both units are displayed. This accommodates both the familiar kilocalorie (kcal) and the metric SI unit, the kilojoule (kJ), for wider international and scientific reference.

To convert from kilocalories to kilojoules, simply multiply the number of kcal by 4.184. For a quick estimate, you can multiply by 4.2.

No, for personal health tracking, it is only necessary to follow one unit consistently. Since most people in the UK think in terms of 'calories' (kcal), sticking with kilocalories is often the easiest approach.

Yes. A key difference is that UK labels require both kcal and kJ, while US labels typically only show 'Calories' (which is equivalent to kcal). US labels also base nutrition data on serving sizes, whereas UK labels use a standard 100g/ml measure.

The traffic light system is a voluntary front-of-pack label used by many UK manufacturers and retailers. It uses red, amber, and green colours to indicate high, medium, or low levels of fat, saturated fat, sugars, and salt, along with the kcal count.

The NHS provides guidance on average recommended daily intakes, suggesting around 2,500kcals for men and 2,000kcals for women, though these can vary by individual needs.