BMR Calculator

1. Choose sex and units. Pick female or male, then metric or imperial. Type your age, weight and height in the units you chose.
2. Add body fat only when you know it. A measured body fat percent unlocks a second estimate based on lean mass. The main result does not need it.
3. Pick a lifestyle. The tool multiplies your BMR by a physical activity level (PAL) to show the energy a full day uses.

Basal metabolic rate is the minimal rate of energy use that keeps the body alive. The FAO/WHO/UNU energy report defines it that way and lists the work it pays for: cell repair, hormones, body temperature, the heart and breathing muscles, and the brain.

BMR is measured, not guessed, in a laboratory. The person lies awake after 10 to 12 hours without food and 8 hours of rest, in a room that causes no shivering or sweating. An equation such as Mifflin-St Jeor predicts that measurement from age, sex, weight and height.

BMR makes up about 45 to 70 percent of the energy an adult uses in a day, according to the same report. Movement and digesting food use the rest. That share is why BMR is the starting point for any calorie estimate.

BMR is not a target for eating. It is one input. Daily needs are higher, because nobody spends a whole day at complete rest.

The calculator applies the Mifflin-St Jeor equation, then scales the result by an activity level.

1. Convert units. Pounds become kilograms (x 0.45359237) and inches become centimeters (x 2.54).
2. Apply Mifflin-St Jeor. Mifflin and colleagues derived the equation in 1990 from 498 healthy adults aged 19 to 78, measured by indirect calorimetry. The paper calls the result resting energy expenditure.
3. Scale by PAL. The FAO/WHO/UNU report gives worked lifestyle examples of PAL 1.53 (sedentary or light), 1.76 (active) and 2.25 (vigorous).
4. Add the lean-mass estimate. With body fat entered, lean mass = weight x (1 - body fat / 100). Cunningham proposed 500 + 22 x lean mass in 1980.

Take a 30-year-old woman who weighs 65 kg and is 165 cm tall.

1. 10 x 65 = 650.
2. 6.25 x 165 = 1,031.25.
3. 5 x 30 = 150.
4. 650 + 1,031.25 - 150 - 161 = 1,370 kcal a day (1,370.25 before rounding).

That is 5,733 kJ a day, or about 57 kcal an hour. With a sedentary or light lifestyle (PAL 1.53) her day uses about 2,096 kcal. An active lifestyle (PAL 1.76) raises that to 2,412 kcal, and a vigorous one (PAL 2.25) to 3,083 kcal.

With a measured body fat of 28 percent, her lean mass is 46.8 kg and the Cunningham estimate is 1,530 kcal a day. The two equations disagree by 160 kcal. That gap is normal and shows why every result is an estimate.

BMR by Weight at Age 30

Values are Mifflin-St Jeor results in kcal a day.

Four inputs move the Mifflin-St Jeor result, and body composition moves the lean-mass result.

Body Weight

Each extra kilogram adds 10 kcal a day. A 30-year-old man of 180 cm gets 1,780 kcal at 80 kg and 1,880 kcal at 90 kg.

Height

Each extra centimeter adds 6.25 kcal a day, so 10 cm adds 62.5 kcal.

Age

Each year subtracts 5 kcal a day. Ten years lower the estimate by 50 kcal when weight and height stay the same.

Sex

At the same age, weight and height, the male result is 166 kcal higher than the female result. The constants +5 and -161 create that gap.

Body Composition

Lean tissue drives resting energy. At 80 kg, the Cunningham estimate is 1,996 kcal with 15 percent body fat and 1,732 kcal with 30 percent, a gap of 264 kcal. Use the body fat calculator for a tape-measure estimate of body fat.

The equations differ in the inputs they need and the people they were built on.

Mifflin and colleagues reported that the Harris-Benedict equations overestimated measured resting energy by 5 percent in their sample. That finding is the reason this tool leads with Mifflin-St Jeor.

Other pages show revised Harris-Benedict or Katch-McArdle numbers. This page leaves them out because we could not confirm their coefficients in an original source.

FAO Lifestyle Categories

The report notes that PAL values above 2.40 are hard to keep up for long.

Estimating Maintenance Energy

BMR x PAL gives a first estimate of the energy that keeps weight stable. The calorie calculator builds a daily target from that kind of figure.

Comparing Two Body Weights

Rerun the tool with a new weight to see how the estimate shifts. A 10 kg change moves the result by 100 kcal a day. The weight loss calculator covers timelines.

Checking a Device or App

Watches and apps report resting calories from a similar equation. A figure far from this one usually means a wrong age, height or weight in the device profile.

Preparing for a Dietitian Visit

Bring the estimate and your inputs. A clinician can order indirect calorimetry when a measured value matters.

1. Treating BMR as a Daily Calorie Target

BMR covers rest only. Daily energy is BMR times a PAL of about 1.4 or more.

2. Mixing Units

Typing pounds while the tool is set to kilograms more than doubles the weight term. Check the unit box first.

3. Picking Too High an Activity Level

Office work with a few short walks is the sedentary or light band. The active band assumes hours on your feet or regular exercise.

4. Guessing Body Fat

The lean-mass estimate is only as good as the body fat number. Leave the field empty without a measured value.

5. Expecting a Measured Value

An equation gives the average for people like you. Two people with the same inputs can differ.

6. Using It for a Child

The study sample was adults. Growth changes energy needs, so a child needs a clinician, not this equation.

The Mifflin-St Jeor equation explained 71 percent of the variation in measured resting energy in its study sample (R squared = 0.71). The rest comes from differences the inputs do not capture.

This page is not a diagnosis. See a clinician for unexplained weight change, constant tiredness or any plan to lose a large amount of weight.

There is no single normal value, because BMR depends on body size, age and sex. At age 30, the equation gives 1,370 kcal a day for a 65 kg, 165 cm woman and 1,780 kcal for an 80 kg, 180 cm man.

Not exactly. BMR is measured under strict conditions after an overnight fast and full rest. Resting metabolic rate is measured under looser conditions. The Mifflin-St Jeor paper predicts resting energy expenditure, and most calculators label it BMR.

BMR is energy at complete rest. TDEE is the total for a real day, found by multiplying BMR by a physical activity level. A BMR of 1,370 kcal becomes about 2,096 kcal at PAL 1.53.

Convert first. Multiply pounds by 0.45359237 and inches by 2.54. A 45-year-old woman of 150 lb and 66 inches is 68.04 kg and 167.64 cm, which gives 1,342 kcal a day.

Yes, in the equation each year of age lowers the estimate by 5 kcal a day. Loss of lean tissue with age is one reason measured values fall.

Other tools use other equations or round the inputs. Harris-Benedict results tend to be higher. Mifflin and colleagues found those equations overestimated measured values by 5 percent in their sample.

This page cannot answer that for you. A calorie target is a medical and personal decision. Talk to a doctor or a registered dietitian before you follow a low-calorie plan.

Body size and lean mass are the inputs that raise the estimate. The equations on this page cannot tell you how your own body will respond to training or diet.

Children, teenagers, pregnant or breastfeeding women and people with an illness that affects metabolism should not rely on it. The equation was built on healthy adults aged 19 to 78.

No. The math runs in your browser. The Save button keeps results only in your own browser storage.

• Mifflin-St Jeor equation: a new predictive equation for resting energy expenditure in healthy individuals (Mifflin MD and others, American Journal of Clinical Nutrition, 1990; PubMed record).
• Cunningham equation: a reanalysis of the factors influencing basal metabolic rate in normal adults (Cunningham JJ, American Journal of Clinical Nutrition, 1980; PubMed record).
• Energy requirements of adults: physical activity levels and lifestyle categories (FAO/WHO/UNU, Human energy requirements, chapter 5).
• Definition of basal metabolic rate and the kilocalorie to kilojoule factor (FAO/WHO/UNU, Human energy requirements, chapter 2).
• Body Weight Planner and typical physical activity levels (National Institute of Diabetes and Digestive and Kidney Diseases).