How to calculate your BMR: the formulas, worked in stones and inches, and how far to trust them

What is BMR, in plain terms?

Your body uses energy even when you do nothing. The NHS lists breathing and keeping your heart beating among the basic functions that use the energy from calories.²

BMR is the name for that resting energy use, measured under set conditions. The Scientific Advisory Committee on Nutrition (SACN) defines it as a standardised measure of metabolism in a basal state.⁴ In practice that means awake, at rest, after all food has been digested and absorbed, and in a thermoneutral environment (neither too hot nor too cold).⁴

It is usually the biggest part of the energy you use in a day. SACN puts it at 40 to 70% of total energy expenditure for most people, depending on age and lifestyle.⁴ The rest is movement, digestion and everything else you do.

Two things BMR is not. It is not a calorie target, and it is not the 2,000 and 2,500 kcal figures you see on NHS pages. Those are average intake guides, covered further down.¹

How to calculate your BMR: the formulas, step by step

Two published equation families are worth knowing. Both start from kilograms and centimetres or metres, so the first job is converting your stones, pounds, feet and inches.

Step 1: convert your units

There are 14 lb in a stone, 1 lb is 0.45359237 kg, and 1 inch is 2.54 cm. So 12 st 7 lb is (12 × 14) + 7 = 175 lb, or 79.38 kg. Rounded kilograms can shift the result slightly, so keep a couple of decimals until the end.

Step 2: pick an equation

Mifflin and colleagues published their equation in 1990. It came from 498 healthy people aged 19 to 78, of normal weight and with obesity, whose resting energy was measured by indirect calorimetry.⁵ The same abstract reports that the older Harris-Benedict equations overestimated measured resting energy by 5%.⁵

• Men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5.⁵
• Women: 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161.⁵

The Henry equations (Henry 2005, Oxford) are the ones SACN uses to estimate BMR.⁴ They draw on 10,552 measured BMR values.⁶ SACN reports that they give values 3 to 4% lower than the older Schofield equations, and that an evaluation in adults found them the more accurate of the two.⁴

SACN prints the Henry coefficients in kcal a day, with weight in kilograms and height in metres. Here they are for adults, from its tables 18 and 19.⁴

Step 3: do the sum and round sensibly

Work the equation, then round to the nearest 10 kcal. Any digit beyond that is false precision, as the next sections explain.

A worked example in stones, feet and inches (and kilograms)

Here are two invented adults, worked through both equations. The numbers are illustrations of the arithmetic, not typical people.

Adult A: a man aged 45, 12 st 7 lb, 5 ft 10 in

12 st 7 lb is 175 lb, which is 79.38 kg. 5 ft 10 in is 70 inches, which is 177.8 cm, or 1.778 m.

• Mifflin-St Jeor: 10 × 79.38 + 6.25 × 177.8 − 5 × 45 + 5 = 1,685 kcal a day.
• Henry, weight and height, men 30 to 60: 11.4 × 79.38 + 541 × 1.778 − 137 = 1,730 kcal a day.
• Henry, weight only, men 30 to 60: 14.2 × 79.38 + 593 = 1,720 kcal a day.

Adult B: a woman aged 35, 10 st 0 lb, 5 ft 5 in

10 st is 140 lb, which is 63.50 kg. 5 ft 5 in is 65 inches, which is 165.1 cm, or 1.651 m.

• Mifflin-St Jeor: 10 × 63.5 + 6.25 × 165.1 − 5 × 35 − 161 = 1,331 kcal a day.
• Henry, weight and height, women 30 to 60: 8.18 × 63.5 + 502 × 1.651 − 11.6 = 1,337 kcal a day.
• Henry, weight only, women 30 to 60: 9.7 × 63.5 + 694 = 1,310 kcal a day.

The two equations land close together here. That says the arithmetic is consistent. It does not say either number is right for a real person, which is the subject of the accuracy section below.

BMR versus total daily energy: where activity comes in

Total energy expenditure is more than BMR. SACN writes it as BMR multiplied by a physical activity level (PAL): TEE equals BMR × PAL.⁴

SACN’s population PAL has a median of 1.63. The 25th and 75th percentiles, for people judged less or more active than average, are 1.49 and 1.78.⁴ These are values for groups. This guide has not found published, sourced labels such as “sedentary” or “very active” attached to specific multipliers, so it does not invent any. Multipliers in the 1.2 to 1.9 range seen on many websites were not checked against a source for this guide and are not used.

Read that table as a demonstration of how the formula works. It is not a calorie target for anyone.

Where the NHS 2,000 and 2,500 figures fit

The NHS says an average man needs 2,500 kcal a day and an average woman 2,000 kcal.¹ It adds that the figure can differ with age, weight, height and how much exercise you do.¹ That is an intake guide for an average person. It is not a BMR, and it is not your total energy expenditure.

A note on dates. The NHS page behind those figures was last reviewed on 17 April 2023 and shows a review date of 17 April 2026 that has now passed.¹ The same figures also appear on a second NHS page with no date.² Treat them as a broad guide and check the NHS page for updates.

For a plainer account of daily burn, including walking and everyday movement, see how many calories you burn in a day. This guide stays with BMR.

Why two people of the same weight can have a different BMR

Weight and height are only a rough proxy for what is going on inside the body. SACN writes that fat-free mass is the principal determinant of differences in BMR between individuals, once body size is allowed for.⁴ It adds that fat mass generally accounts for a small amount of that variation.⁴

Other points SACN makes:

• Larger people have more tissue mass and so a higher BMR.⁴
• BMR declines with older age, mainly because of the gradual loss of fat-free mass.⁴ SACN adds that it is unclear whether the change is entirely a result of body composition.⁴
• Weight gain contains a higher share of fat-free mass in men than in women, so BMR rises more with body mass index in men.⁴

An illustration with fat-free mass

Mifflin and colleagues also published an equation based on fat-free mass (FFM): REE = 19.7 × FFM (kg) + 413. They found FFM to be the best single predictor in their 1990 sample.⁵ They also reported that adding body weight distribution did not significantly improve the prediction.⁵

Take two invented adults who each weigh 12 st 7 lb (79.38 kg). The first is 30% body fat, so fat-free mass is 70% of 79.38 kg, which is 55.57 kg. The second is 20% body fat, so fat-free mass is 80%, or 63.50 kg.

A weight-and-height equation would give these two people the same answer, because it never sees the difference. That is the main reason body composition matters here. If you want to understand body fat and lean mass first, start with what body composition is and body fat percentage. To see how muscle fits in, read muscle mass, and for a related and often misunderstood number, metabolic age. If you are comparing ways to measure body composition, see DEXA scan vs smart scale.

This guide gives no figure for how many calories a pound of muscle burns, because none was read in the sources used.

How accurate is any BMR number?

Less than the tidy numbers suggest. Four points from the evidence read.

1. SACN says it does not appear there has been any recent validation of the Henry equations within the current UK population.⁴ It also says its reference values should not be applied to individuals.⁴
2. In one comparison SACN cites, using 767 American adults aged 20 to 96, 73% were predicted within 10% of measured BMR by the Henry weight and height equation, against 69% for Schofield and FAO.⁴ So even the better equation missed by more than 10% for roughly one person in four in that sample.
3. The Mifflin equation was built in 1990 on a sample of 498 people.⁵ Its authors reported an R squared of 0.71.⁵ The abstracts read for this guide give no individual-level error range.
4. Henry’s 2005 paper says the older Schofield and FAO equations overestimate BMR in many communities.⁶ That is why newer equations exist, but it also shows that the choice of equation changes the answer.

Abstracts and a population report are not the full papers. This guide did not read the full text of Mifflin 1990 or Henry 2005, so it does not quote their error tables.

In short: use a BMR calculation to understand how the pieces fit, not as a measurement. The sums cannot see your fat-free mass.

One more caution. The NHS body mass index tool tells you whether your weight is healthy for your height. It cannot tell the difference between muscle and fat.¹⁰ BMR equations share that blind spot. For BMI itself, see BMI and healthy weight.

This guide did not find an NHS BMR calculator. A search of the NHS site for basal metabolic rate returned no calculator,¹³ so it says nothing about one.

What to do with your BMR (and what not to do)

A BMR estimate is useful for understanding. Using it to set a strict daily limit is where problems start.

• Do not set your calorie intake equal to your BMR as a weight-loss plan. The NHS Better Health advice is to reduce intake by around 600 calories a day from what you eat now, not from your BMR.²
• Aim for gradual change. The NHS suggests losing 1 to 2 lb (0.5 to 1 kg) a week and advises against losing weight suddenly through diets.³ That NHS page was last reviewed on 17 March 2023 and its review date of 17 March 2026 has passed, so check the live page.
• Low-energy diets of 800 to 1,200 kcal a day are, in NICE guidance, only for people with obesity, in a specialist service with long-term support.⁷ Very-low-energy diets of under 800 kcal are for a specialist obesity service only.⁷ They are not something to start from a calculator.
• NICE also advises keeping total energy intake below energy expenditure for dietary approaches.⁷ Working out your own expenditure from a formula is imprecise, which is another reason to ask a professional for a plan.
• Do not treat a low or high BMR as a diagnosis. Nothing read for this guide gives a “good” or “normal” BMR range for adults in the UK, so this guide gives none.

Can you raise your BMR? SACN names fat-free mass as the main driver of differences between people.⁴ No source read for this guide puts a number on what a gain in muscle does to BMR, so this guide makes no promise. Treat any claim of a quick metabolic boost with caution.

If counting numbers worries you

Some people find calorie sums harmful. The NHS describes spending a lot of time worrying about your weight and body shape, or eating very little, as possible signs of an eating disorder.⁸ Beat, the UK eating disorders charity, calls eating disorders serious mental illnesses that affect people of all ages, genders and backgrounds, and runs a helpline.⁹ If this sounds familiar, skip the calculations and speak to a GP.

Frequently asked questions