BMR Calculator

What Is BMR?

Being alive costs calories before you spend any on the day. A resting body still pumps blood, moves air, filters plasma, rebuilds tissue and holds its own temperature against the room, and that continuous cost is basal metabolic rate. For most adults it is the largest single line in the daily energy budget.

The FAO/WHO/UNU expert consultation on human energy requirements puts BMR at roughly 45 to 70 percent of total daily energy expenditure in adults, determined principally by sex, body size, body composition and age. Three of those four are what this page asks you for. The fourth, composition, is the one the equation has to assume on your behalf.

The word basal is doing real work in that definition. A genuine BMR measurement carries strict conditions: the same consultation specifies being awake and lying supine, 10 to 12 hours after a meal, following eight hours of physical rest with no strenuous exercise the previous day, mentally relaxed, in a room warm enough that you are neither shivering nor sweating. Almost nobody meets that description outside a laboratory, which is why the figure here is derived from other people's measurements rather than read off yours.

BMR vs RMR: Why the Two Terms Get Swapped

Resting metabolic rate is the same quantity measured under looser rules — a comfortable 10-to-20-minute rest rather than the overnight fast and eight hours of physical rest the basal protocol demands — and it comes out slightly higher than a strict basal reading for exactly that reason.

The distinction matters here because of where this equation came from. Mifflin and colleagues titled their 1990 paper a predictive equation for resting energy expenditure, and the systematic review that later endorsed it discusses resting metabolic rate throughout. What this page labels BMR is, strictly, a prediction of resting energy expenditure. Everyday usage treats the terms as interchangeable and so does this calculator, but a clinician quoting a measured BMR is describing a stricter test than the one behind these numbers.

How unforgiving that test is shows up in the protocol. The evidence review behind current dietetic practice found that food, alcohol, caffeine and nicotine each shift resting metabolic rate for a variable number of hours afterward, that moderate or vigorous exercise carries over longer still, and that a valid reading needs a 10-minute measurement with the first five minutes discarded. An equation asks four questions instead, and gets an answer that is good on average and exact for nobody.

How Much of Your Day BMR Accounts For

Total daily burn is BMR multiplied by an activity factor, so the share your resting rate represents shrinks as the factor rises. The figures below belong to one reference body used throughout this page — a 30-year-old man at 175 cm and 70 kg, whose calculated BMR is 1,649 — at the five standard multipliers.

Even at the top of that ladder more than half the daily total is the floor, and at the sedentary setting it is 83 percent. That is the practical reason a new training program changes daily calorie needs less than people expect: the exercise is added to a base that was already doing most of the work.

Those five totals are the result of multiplying, and the multiplying is done for you — along with a choice of five different resting equations — on the TDEE Calculator.

How Do You Calculate BMR?

A single linear equation does the whole job. Weight, height and age each carry a fixed coefficient, and sex changes only the constant on the end.

BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + s

where s = +5 for men and −161 for women

The Mifflin-St Jeor Formula, Written Out

Split by sex, the two versions differ by one number: 166 calories, the gap between +5 and −161.

Men:   BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5

Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

Both expect metric units. Enter pounds or feet and inches and the calculator converts before the equation runs — a pound becomes 0.45359237 kg and an inch becomes 2.54 cm — so the arithmetic above is always what happens underneath.

Mifflin's paper also published a combined form, REE = 9.99 × weight + 6.25 × height − 4.92 × age + 166 × sex − 161, with sex scored 1 for men and 0 for women. The authors reported that rounding the coefficients and separating the equation by sex did not affect its predictive value, and it is the simplified pair above that dietetic practice adopted.

What Each Coefficient Is Worth

Because the equation is linear, every coefficient converts straight into calories, and the conversion does not change with the size of the person.

That last line has a consequence you can check on the calculator above. A 30-year-old man at 175 cm and 70 kg returns 1,649. A 30-year-old woman at the same 175 cm returns the identical 1,649 at 86.6 kg — 16.6 kg heavier, because 166 calories of constant divided by 10 calories per kilogram is 16.6 kilograms.

• Each kilogram of body weight adds exactly 10 calories a day.
• Each centimeter of height adds exactly 6.25 calories a day.
• Each year of age subtracts exactly 5 calories a day.
• Being male rather than female adds exactly 166 calories a day, all of it in the constant.

Step by Step

The form asks six questions in a fixed order. Four of them change the answer; the two unit selectors only change how your entry is read.

Sex, height unit and weight unit open preselected on Male, Centimeters and Kilograms. Age, height and weight open blank, so nothing is calculated until all three are filled in and the button is pressed.

• Choose Male or Female. This sets the constant, +5 or −161.
• Enter your age in whole years. The tool accepts 15 to 100.
• Choose your height unit: Centimeters, or Feet + inches written as 5.10 for 5 ft 10 in.
• Enter your height in the unit you just chose.
• Choose your weight unit: Kilograms or Pounds.
• Enter your weight in that unit, then press Calculate.

Worked Example: 30-Year-Old Man, 175 cm, 70 kg

Male, 30 years, 175 cm, 70 kg, entered in metric units.

BMR = (10 × 70) + (6.25 × 175) − (5 × 30) + 5

BMR = 700 + 1,093.75 − 150 + 5

BMR = 1,648.75 → 1,649 kcal/day

Basal metabolic rate

1,649 kcal/day

Two lines follow that readout in the panel. The first restates the arithmetic with his own figures in it, as 10×70.0 + 6.25×175 − 5×30 + 5. The second divides the total by 24 to give 69 kcal/hour — about 1.1 calories a minute, spent whether he is asleep, reading or stuck in traffic.

Worked Example: 30-Year-Old Woman, 165 cm, 60 kg

Female, 30 years, 165 cm, 60 kg. The constant changes, and so do the first two terms, because the body is smaller as well.

BMR = (10 × 60) + (6.25 × 165) − (5 × 30) − 161

BMR = 600 + 1,031.25 − 150 − 161

BMR = 1,320.25 → 1,320 kcal/day

Basal metabolic rate

1,320 kcal/day

Her panel shows 55 kcal/hour, and her underlying figure sits 328.5 below the reference man's — 1,320 against 1,649 once both are rounded for the readout. That gap breaks down cleanly: 166 from the sex constant, 100 from the 10 kg of weight and 62.5 from the 10 cm of height. None of it is metabolism as such — it is three measurements and a constant.

Entering Feet, Inches, and Pounds

The Feet + inches option reads the digits after the decimal point as whole inches, not as a fraction of a foot, and the selector label spells the convention out: 5.10 = 5 ft 10 in. Missing that is the most common way to get a wrong answer from this page.

Typing 5.1 when you meant five foot ten costs 143 calories. Keep the trailing zero, or switch the selector to Centimeters and the ambiguity disappears. Inches above 11 are clamped rather than carried over, so 5.12 stops at 5 ft 11 in instead of becoming 6 ft 0 in.

The weight selector deserves the same glance before you trust a surprising number. A 30-year-old man at 175 cm who types 154 while it still reads Kilograms gets 2,489 instead of the 1,647 that 154 pounds actually produces. One unclicked control moves the answer by 841 calories. The reverse mistake is quieter: 70 entered with the selector on Pounds is read as 31.8 kg and returns 1,266.

Mixed units are fine as long as each selector matches what you typed. Feet + inches 5.9 with 154 pounds returns 1,649, the same answer as 175 cm with 70 kg, because 5 ft 9 in is 175.26 cm and 154 lb is 69.85 kg.

BMR Chart: Resting Calories by Height, Weight, and Age

Every figure below came out of the calculator on this page.

The grid below is for men aged 30, in calories per day. Find the cell nearest your own build to see roughly where your answer will land before you enter anything.

Read across as well as down and the shape of the equation appears. Ten kilograms is worth 100 calories on every single row, while the entire 20 cm span of height is worth 125. Weight moves this number several times harder than height does.

BMR Chart for Women

The same grid for women, again at age 30. The constant is 166 lower, so a woman and a man of identical height, weight and age are always exactly 166 calories apart.

Between them the two grids span 1,158 to 2,111 calories a day, and that is with age pinned at 30 and no body outside 50 to 110 kg. It is a wide floor. Comparing your figure against someone else's, without their height, weight, age and sex attached, tells you almost nothing.

What Age Does to the Number

Age enters as a flat minus 5 calories per year, so the decline this equation models is a straight line. Below, the two reference bodies are held constant and only the birth year moves.

Fifty years of aging costs 250 calories a day at a fixed body weight, which is less than the 328.5 separating the two reference bodies at the same age. The equation treats that decline as a property of age itself, and that is a simplification: a large share of the real fall comes from losing muscle, and losing muscle is not compulsory.

How Much Each Field Moves the Result

Changing one field at a time on the reference man shows what each entry is actually worth, and where care with the tape measure pays off.

The two ten-centimeter rows look inconsistent — plus 62 up against minus 63 down — and that is display rounding rather than a fault. Ten centimeters is worth exactly 62.5 calories, and the reference figure is 1,648.75, so adding lands on 1,711.25 and subtracting on 1,586.25. Both of those round down to a whole calorie while 1,648.75 rounds up to 1,649, and that is where the missing calorie goes. Weight is the field worth measuring carefully. A kilogram is 10 calories, a centimeter 6.25, a year 5 — so being 2 kg out on the scale costs you more accuracy than being 3 cm out on your height, and both are small beside the body composition the equation never sees.

Using the Free BMR Calculator Online

The tool at the top of this page is free, needs no sign-in and runs one equation. Press Calculate and the arithmetic happens inside the page: the browser loads a small formula module on demand and multiplies locally, so no server round trip sits between your entry and your answer.

Six fields, four of which carry your measurements. There is no formula selector, no activity dropdown, no body-fat field and no goal setting. This page performs one calculation and hands back one number.

• Sex — Male or Female
• Age — in years, 15 to 100
• Height Unit — Centimeters, or Feet + inches (5.10 = 5 ft 10 in)
• Height — in the unit selected
• Weight Unit — Kilograms or Pounds
• Weight — in the unit selected

What the Result Panel Shows

The panel is headed Basal Metabolic Rate and returns four lines. For the reference man they read as follows.

The second line is worth reading rather than skipping past, because it is the quickest check that your units landed where you meant them to. Weight appears there already converted to kilograms, so 154 pounds shows as 10×69.9. If it shows 10×154.0 instead, the selector was still on Kilograms.

• 1,649 kcal/day, as the large readout
• Mifflin-St Jeor: 10×70.0 + 6.25×175 − 5×30 + 5 — the arithmetic with your own numbers in it
• That's 69 kcal/hour just existing — before any movement
• Multiply by an activity factor (1.2 sedentary … 1.9 very active) for daily needs — see the table below

A Copy result button below the readout puts all four lines on the clipboard as plain text. Should an entry fall outside what the equation will accept, the panel turns amber under a Check your inputs heading and shows one of three messages in place of a number.

What the Calculator Does Not Ask For

Knowing what is missing tells you which claims about your result are safe to make.

The last of those is a decision rather than a shortfall. The 2005 systematic review of the four equations dietitians actually use — Harris-Benedict, Mifflin-St Jeor, Owen, and WHO/FAO/UNU — found Mifflin-St Jeor the most reliable, predicting resting metabolic rate within 10 percent of the measured value in more people, obese and nonobese alike, than any other, and with the narrowest error range. A menu here would mostly offer worse answers.

• No body-fat percentage — nothing here measures or accepts composition
• No activity level — the answer is a resting floor, never a daily total
• No goal — no deficit or surplus is applied to the figure
• No choice of equation — Mifflin-St Jeor is the only one this page runs

Composition is the one determinant these six fields cannot reach, and a tape-measure estimate of it is the usual starting point. That is what you get from the Body Fat Calculator.

How to Read Your BMR Result

The number is calories per day at complete rest. It is not a target, not a score and not the amount you should eat. It is the base of an energy budget, and everything useful you do with it is arithmetic performed on top of it.

Is My BMR Normal?

There is no normal BMR in the sense that there is a normal blood pressure, because the figure scales with the body carrying it. Across the two charts above — age fixed at 30, weights from 50 to 110 kg — the answers run from 1,158 to 2,111 calories a day, and every one of them is right for the body it describes.

Per kilogram is the more informative comparison. The reference man burns 23.6 calories per kilogram of body weight per day; a 110 kg man of the same height and age burns 18.6. The heavier body has the larger BMR and the smaller rate, because the constant and the height term are spread across more mass. A big BMR is mostly evidence of a big body, not a fast metabolism.

For a sense of scale rather than a judgment on you, the NHS quotes 2,500 kcal a day for an average man and 2,000 for an average woman. Those are totals including activity, not resting figures, which is why a BMR of 1,649 sitting well below 2,500 is behaving exactly as it should.

Turning BMR Into a Calorie Target

Three steps separate a resting figure from something you can eat to, and only the first is arithmetic the equation can do for you.

Do not eat at your BMR by accident. It is a stay-in-bed number, so for the reference man it already sits 330 calories below the lowest maintenance estimate the multipliers produce and 907 below the moderate one. Treating it as a daily target quietly builds a deficit nobody chose.

• Multiply BMR by an activity factor between 1.2 and 1.9 for maintenance. The reference man's 1,649 becomes 1,979 sedentary or 2,556 at the moderate 1.55.
• Subtract for fat loss or add for gain. The size of that adjustment is a plan you choose, not a result the equation produces.
• Eat at the figure for two to three weeks, weigh yourself daily, and correct the multiplier against the weekly average rather than against the equation.

For a deficit sized to a rate of loss instead of a round number, carry the maintenance figure into the Calorie Deficit Calculator.

Your BMR Changes as Your Weight Does

A BMR figure has a shelf life. Each kilogram is worth 10 calories in the equation, so a 30-year-old man at 175 cm who goes from 90 kg to 80 kg watches his estimate fall from 1,849 to 1,749. Any plan built on the higher number is a hundred calories too generous by the time he arrives.

Recalculate after every four to five kilograms, or roughly every six weeks on an active diet. The habit also heads off a common misreading: a falling BMR during weight loss is not a metabolism breaking down, it is a smaller body needing less, and the equation says so in advance.

How much muscle survives the diet is the part of that fall you can influence. Fat-free mass explained 63 percent of the variation in measured BMR among the 150 adults in Johnstone's 2005 study, against 6 percent for fat mass and 2 percent for age. Losing weight as fat rather than as lean tissue is what keeps the floor from dropping further than it needs to.

Limits: Where a BMR Estimate Breaks Down

The page returns a confident whole number, and that confidence is not fully earned by the method behind it. Three limits sit between this estimate and your actual resting burn, and none of them is visible in the answer. A fourth constraint is visible: the range of entries the form will accept at all.

It Cannot See Your Body Composition

Weight, height, age and sex are proxies for the thing that actually drives resting metabolism, which is how much of you is not fat.

Mifflin's own paper makes the point. Alongside the equation this page runs, the authors reported that fat-free mass was the best single predictor of resting energy expenditure in their 498 subjects: REE = 19.7 × fat-free mass + 413. Apply that to a single 70 kg body at a range of body-fat levels and the answers separate.

The right-hand column is the same 30-year-old man at 175 cm and 70 kg at every one of those compositions, because no field on this page could tell them apart. The left-hand column moves 345 calories across the same range. Read the two columns as a contrast in information, not as a like-for-like accuracy test: the fat-free-mass equation was fitted across all 498 subjects of both sexes, while this page runs the male-specific one, so the two are not measuring against the same baseline.

The practical consequence is a predictable direction of error. The estimate runs low for a visibly muscular body and high for a soft one of the same weight, and neither person can tell from the number which of them they are.

Dieting Lowers Resting Burn More Than the Equation Predicts

A linear equation assumes your resting rate depends only on the body you have today. Two of the better-known studies in energy balance say the history of that body matters too.

Leibel, Rosenbaum and Hirsch measured 18 obese and 23 never-obese subjects at their usual weight and again after experimental weight change. Holding a weight 10 percent or more below the starting point was associated with a fall in total energy expenditure of 6 ± 3 kcal per kilogram of fat-free mass per day in the never-obese group and 8 ± 5 in the obese group, with resting and nonresting expenditure each accounting for 3 to 4 of it. That reduction was over and above what the smaller body itself predicted.

The follow-up on The Biggest Loser contestants is the extreme version of the same finding. Six years after the competition, the 14 participants studied had regained 41.0 ± 31.3 kg of the 58.3 ± 24.9 kg they lost, yet their measured resting metabolic rate was still 704 ± 427 kcal a day below baseline — a metabolic adaptation of −499 ± 207 kcal a day once body composition and age were adjusted for.

Neither result makes this equation useless, and neither describes an ordinary diet. What they establish is a direction: after substantial weight loss, expect your true resting rate to sit below what this page predicts for your new weight, and read a stalled plan as information rather than as failure.

People the Equation Was Not Built For

The equation came from one specific sample, and its authors and reviewers are explicit about who was in it.

Children and adolescents need age-specific equations this page does not carry, and pregnancy and breastfeeding add requirements no BMR equation includes. Thyroid disease shifts resting metabolism directly — the NIDDK notes that thyroid hormones control the way the body uses energy, and that nearly 5 out of 100 Americans aged 12 and over have hypothyroidism, most cases mild or with few obvious symptoms. Fever, recent large weight loss and a long list of medications move the same number.

• 498 healthy adults aged 19 to 78 — 251 men and 247 women, 264 of normal weight and 234 with obesity — with resting energy expenditure measured by indirect calorimetry.
• Weight, height, age and sex together explained 71 percent of the variation in that sample, leaving 29 percent these four fields cannot reach.
• The 2005 review that endorsed the equation noted that older adults and US-residing ethnic minorities were underrepresented both in deriving predictive equations and in validating them.
• Nobody under 19 was in the derivation sample, although this calculator will accept an age as low as 15.

Johnstone's 2005 study adds something worth knowing before you compare your figure with anyone else's: 26 percent of the between-subject variation in measured BMR was left unexplained after fat-free mass, fat mass, age, sex and bone mineral content had all been accounted for. Circulating thyroxine explained a quarter of that residual in men and none of it in women. Part of the spread between two apparently identical people is real, and nothing you can type here will find it.

The Values the Tool Will Accept

Three ranges are enforced before the equation runs, and each has its own wording in the amber Check your inputs panel.

Those bounds catch the worst unit mistakes for you. Enter 175 while the height selector reads Feet + inches and it is read as 175 feet, far past the ceiling, so the amber panel appears instead of a wrong answer. Enter 5.10 while the selector reads Centimeters and 5.1 cm fails the floor in the same way.

Inside the ranges the tool will calculate anything, including combinations no real body occupies. It is an equation, not a screening test, and it holds no opinion on whether your entries are plausible — one more reason to treat the output as a starting figure and let a few weeks of your own data correct it.