BMR Calculator UK

Which calculator should you use?

Start by naming the quantity you want to understand. If you want to inspect a resting-energy equation, use the BMR calculator on this page. If you want to see what happens after including an assumed activity factor, use the TDEE calculator. If you are comparing a food label written in kilojoules with one written in kilocalories, use the energy converter. These tools share some vocabulary, but they answer different questions.

A BMI result cannot be used in place of a resting-energy estimate. BMI has units of kilograms per metre squared, while this tool produces kilocalories per day. Likewise, a food’s energy content is an amount of energy, whereas a daily estimate is an amount per day. Keeping the units attached to each number is a simple way to prevent these mix-ups before they affect a calculation.

How to enter UK and metric measurements

The UK option separates height into whole feet and additional inches, and weight into whole stones and additional pounds. For eleven stone four pounds, enter 11 and 4. Do not enter 11.4 in the stones box: the part after a decimal point is a fraction of a stone, not a count of pounds. For five feet nine inches, enter 5 and 9 rather than 5.9 feet.

The metric option uses total centimetres and total kilograms. A height of 1.75 metres becomes 175 centimetres. A weight of 70 kilograms stays 70; it should not be converted to pounds first. Switching the unit buttons converts valid existing measurements so you can inspect the equivalent values. If a field is empty or invalid, check the visible measurements after switching before submitting the form.

Our UK example of eleven stone four pounds becomes 158 pounds. Multiplying by 0.45359237 gives 71.66759446 kilograms. Five feet nine inches becomes 69 inches, or 175.26 centimetres. Those converted values enter the same equation used by the metric option. The unit selector changes the input format, not the underlying prediction method. See the measurement guide for further examples.

A complete UK calculation you can reproduce

Consider a fictional 35-year-old adult who enters eleven stone four pounds, five feet nine inches, and the published male coefficient. This example is invented to demonstrate the arithmetic. It is not a report about a client or a suggested target for a reader with similar measurements.

After conversion, the weight term is 10 × 71.66759446 = 716.6759446. The height term is 6.25 × 175.26 = 1,095.375. The age term is 5 × 35 = 175. Combining them gives 716.6759446 + 1,095.375 − 175 + 5 = 1,642.0509446. The resting result displays as approximately 1,642 kcal/day.

If the same fictional measurements use the published female coefficient, the constant changes from +5 to −161. The resulting estimate is 1,476.0509446 kcal/day. The 166-calorie difference comes from a coefficient in the equation, not from observing either person. The published formula cannot describe every individual variation in body composition or hormonal context.

To audit the example, first reproduce it in UK units. Then switch to metric and check the converted measurements before recalculating. Very small display differences can occur if you manually shorten the converted inputs. Keep more decimal places during a manual check, and round the final answer rather than each term.

What changes when you edit one input?

An equation has predictable mathematical behaviour. Holding everything else constant, adding one kilogram adds 10 kcal/day to this estimate. Adding one centimetre adds 6.25 kcal/day. Adding one year subtracts 5 kcal/day. These statements describe the formula’s coefficients. They are not a promise that a person’s measured metabolism changes by exactly those amounts.

This difference between a model and a person matters when interpreting a table. A table that varies age while fixing height and weight is an illustration of an equation, not a survey of average people at each age. The small table in the sidebar is labelled accordingly. It should not be used to decide that everyone aged 40 has the same resting expenditure.

This is also a useful troubleshooting exercise. Change only one input and predict the difference before calculating. If a much larger difference appears, inspect the units, the other fields, and whether you are reading resting energy or an activity-adjusted output.

From resting energy to an activity scenario

The activity table applies several multipliers to the same unrounded resting estimate. Using the fictional UK result above, a factor of 1.2 produces approximately 1,970 kcal/day. A factor of 1.55 produces approximately 2,545 kcal/day. These are alternative scenarios created by multiplication; the table has not measured how active the fictional adult is.

That distinction is why the tool does not automatically label the selected result as an eating target. Choosing a factor requires assumptions about a pattern of activity, and a personal nutrition decision requires additional context. The table is useful for seeing sensitivity: a change in one uncertain factor can move the output substantially even when the height, weight, and age stay exactly the same.

If another website reports a different daily estimate, compare its numerical multiplier, not just words such as “light” or “moderate.” Also check whether it adds exercise separately. A workout represented in the activity factor should not simply be counted again without understanding the model. The activity-multiplier guide explains this comparison in more detail.

Troubleshoot an unexpected BMR result

When a result looks implausible, begin with the input format rather than a health conclusion. Check whether the weight field expects kilograms, total pounds, or a combination of stones and pounds. Check whether height is requested in centimetres or separate feet and inches. Confirm the age and coefficient selection. It is easy to carry a unit assumption from one website into another.

If the calculator refuses an entry, read the field message. The energy tools accept ages 19–78 and enforce basic height and weight boundaries. Those restrictions help prevent obvious input errors and keep the age range aligned with the original study. They do not certify that every accepted combination is clinically suitable. Do not invent a different age or measurement just to get past validation.

If you change an input, the earlier result disappears until you calculate again. This avoids showing a number from an old set of measurements beside new fields. Reset restores a clearly labelled example; it does not retrieve a saved personal profile. The site’s own calculator code does not save your inputs to a server or create a personal history.

For a suspected arithmetic error, make a small, non-identifying example and record the inputs, equation, expected intermediate terms, and displayed result. That gives a reviewer something reproducible. Repeatedly refreshing a page or comparing screenshots without their inputs is unlikely to reveal the cause.

What an online BMR result cannot establish

A calculator can implement an equation correctly and still be an unsuitable guide for a particular clinical situation. Its inputs do not include a physical examination, detailed body composition, medication history, pregnancy status, or the circumstances of illness and recovery. A correct sum does not fill in information that the model never collected.

The Mifflin–St Jeor paper describes a resting-energy prediction equation. It does not validate every use to which a modern website might put that number. Calling the output “BMR” for familiarity should not turn it into a diagnosis, a guaranteed daily requirement, or a universal lower boundary for food intake. The quantity estimated here is resting energy expenditure.

Use qualified individual advice for pregnancy, breastfeeding, treatment-related nutrition, or eating-disorder care. If numerical tracking is distressing, stop using the tool rather than trying to perfect the output. The educational value is understanding a method and its limits. It is not a requirement to monitor or control your body through a website.

A useful way to record the calculation

If you need to discuss a result, keep the assumptions with it. A concise record can include the tool name, calculation date, measurement units, entered values, equation coefficient, resting result, and any activity factor. Write “estimated REE” or “activity scenario” beside the output. This prevents someone reading the note later from mistaking the number for a measured quantity or prescribed diet.

For the fictional example in this article, a clear note would be: “Mifflin–St Jeor; age 35; 11 st 4 lb; 5 ft 9 in; male coefficient; estimated REE approximately 1,642 kcal/day.” If you also write down the 1.55 scenario, label it separately as approximately 2,545 kcal/day and state that the factor was assumed.

Keep such a record only if it serves a useful purpose for you. Do not post private health details publicly to ask a software question. For general calculation checks, the invented examples in the worked-example collection are sufficient.