Calorie Calculator
🇬🇧 United Kingdom version
Shop labels in the United Kingdom print energy twice, in kilojoules and in kilocalories, so this page shows every result in both. Enter age, gender, height and weight (stones and pounds are the starting unit) and it estimates resting energy, daily energy and a target with gram figures for protein, carbohydrate and fat.
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Energy is shown as kilojoules and kcal, as food labels here give it. 1 kcal = 4.184 kJ. The nutrition declaration must give energy in both kJ and kcal, per 100 g or 100 ml.
Understanding Your Results
United Kingdom rules and figures
- The Food Standards Agency says a UK nutrition declaration must give energy in both kJ and kcal, per 100 g or 100 ml, so neither unit is optional on a pack.
- This page therefore prints each energy figure as kJ first and kcal second, for example 6,309 kJ / 1,508 kcal for the example target.
- Body weight starts in stones and pounds on the UK page and height in centimetres, with 11 st 0 lb and 170 cm as the sample profile.
- One kcal is 4.184 kJ in the calculation, so a 500 kcal adjustment for a loss or gain goal is 2,092 kJ a day.
Sources: Food Standards Agency: Nutrition labelling (checked 2026-11-08)
How the calorie calculator works
Resting energy comes from the equation you pick, daily energy multiplies it by an activity factor between 1.2 and 1.9, and the target moves 500 kcal for a loss or gain goal. All of it is held in kcal; the kJ figure beside it is the kcal figure times 4.184.
BMR = 10 × 63.5 + 6.25 × 165 − 5 × 42 − 161 = 1,295 kcal; daily energy = 1,295 × 1.55 = 2,008 kcal; target = 2,008 − 500 = 1,508 kcal = 6,309 kJ
- Stones and pounds are changed to kilograms before the equation runs, so 10 st 0 lb is used as 63.5 kg and 11 st 0 lb as 69.9 kg.
- Each energy result reads like 6,309 kJ / 1,508 kcal, matching the way a UK nutrition declaration pairs the two units.
- Protein takes 25% of the target at 4 kcal a gram, fat takes 30% at 9 kcal a gram and carbohydrate takes the remaining 45% at 4 kcal a gram.
- Fibre is half a gram for each kilogram you weigh, while the water goal multiplies kilograms by 35 mL.
- Switching the weight list to kg or lb, or the height list to ft/in, keeps your pick on later visits.
How to use the calorie calculator
- Enter your details. Type age, choose male or female, then give height in centimetres and weight in stones and pounds. Each has a small unit list if you think in feet, inches or kilograms.
- Choose how active you are. Pick one of five levels from Sedentary at 1.2 to Extremely active at 1.9. Lightly active at 1.375 is selected to begin with.
- Say whether you want to change weight. Maintain keeps daily energy as it is, while the lose and gain choices subtract or add 500 kcal, which is 2,092 kJ.
- Compare equations. Mifflin-St Jeor starts selected. Harris-Benedict and Katch-McArdle are one tap away, and Katch-McArdle adds a body fat box.
- Fine-tune the grams. Open Settings to type your own protein or fat grams. Carbohydrate takes whatever energy is left.
Example: A 42-year-old woman, 10 st 0 lb, 165 cm, losing weight
Selecting Moderately active and Mifflin-St Jeor gives 5,418 kJ / 1,295 kcal at rest and 8,401 kJ / 2,008 kcal over a whole day. Lose weight sets the target to 6,309 kJ / 1,508 kcal, split into 94 g protein, 170 g carbohydrate and 50 g fat. Her fibre target is 32 g, and 2,223 mL of water comes from 63.5 kg times 35.
When to use the calorie calculator
- Comparing equations for the same person. Switch the BMR formula and watch the maintenance figure move by about 65 kcal between Mifflin and Harris-Benedict.
- Turning a goal into gram targets. Read protein, carbohydrate and fat grams for the goal calories instead of working out the percentages by hand.
- Using a body-fat reading. Enter a body fat percentage under Katch-McArdle if you have a measurement and want the lean-mass-based estimate.
- Logging meals against the target. On the Meal Tracker tab, add foods from a built-in list of ten and compare the day's calories with the goal.
What the calorie calculator does not do
- The loss and gain goals always shift energy by exactly 500 kcal (2,092 kJ), whatever your size, and the 1 lb (0.5 kg) a week label is a rule of thumb rather than a prediction.
- The Meal Tracker uses a built-in list of ten foods only, such as chicken breast, brown rice and avocado half; there is no food database search beyond that.
- A meal you remove moves to a Recently deleted list under Today's Meals, where it can be restored.
- The Insights text on the Progress tab, such as the on-track message, is fixed wording rather than derived from your data.
- Foods and logged meals are held in kcal and converted to kJ for display, so a kJ total can differ by a unit from a label that rounds before converting.
When something else is a better fit
- When you want to set protein, carb and fat ratios by percentage or diet style, use the Macro Calculator.
- When you want calories burned by a specific workout, use the Exercise Calories Calculator.
- When you need a calorie plan for a medical condition, use a registered dietitian, who works from your tests and history rather than a general equation.
Questions about the calorie calculator
Why are there two energy numbers on the UK page?
UK nutrition declarations give kJ and kcal together, so results do the same. A target of 1,508 kcal reads 6,309 kJ / 1,508 kcal. Use whichever unit your food packs make easier to compare.
Can I enter my weight in kilograms instead of stones?
Yes. Use the small list above the weight box to switch to kg or lb. The page starts in stones and pounds, keeps the unit you choose, and converts to kilograms before calculating.
How is a 500 kcal change shown in kJ?
A 500 kcal difference equals 2,092 kJ using 4.184 kJ per kcal. For the example woman, the maintenance figure of 8,401 kJ falls to 6,309 kJ when Lose weight is chosen.
Does the calculator know my GP or dietitian advice?
No. It applies a general equation to the numbers you type. If you have a medical condition or are pregnant, speak to your GP or a registered dietitian rather than relying on a general estimate.
Why does Katch-McArdle match Mifflin-St Jeor for me?
The Body Fat Percentage box was probably empty. Without a value the tool uses Mifflin-St Jeor instead, so the two show the same resting energy.