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BMR Calculator

Find out how many calories your body burns at rest with the Mifflin-St Jeor, Harris-Benedict or Katch-McArdle formula, plus your daily needs by activity level.

Level: Grades 6–7

  • Common Core standard 6.EE.A.2.cEvaluate expressions at specific values of their variables. Include expressions that arise from formulas used in real-world problems. Perform arithmetic operations, including those involving whole-number exponents, in the conventional order when there are no parentheses to specify a particular order (Order of Operations).
  • Common Core standard 6.RP.A.3.dUse ratio reasoning to convert measurement units; manipulate and transform units appropriately when multiplying or dividing quantities.
Printable worksheet

BMR Calculator

Inputs
Equation
Units
Sex

The published equations have separate versions for males and females.

These equations were developed for adults.

Result

Basal metabolic rate (Mifflin-St Jeor)

1,758 kcal/day

Estimated BMR: about 1,758 kcal per day (Mifflin-St Jeor). This is an estimate, not a measurement.

Per hour at rest
73.2 kcal/hour
Harris-Benedict (1984), for comparison
1,837 kcal/day

See the step-by-step solution ↓

Estimated daily calories by activity level (BMR × activity factor)
Estimated daily calories by activity level (BMR × activity factor)
Activity levelFactorCalories per day
Sedentary: little or no exercise1.22,109
Lightly active: exercise 1–3 days a week1.3752,417
Moderately active: exercise 3–5 days a week1.552,724
Very active: hard exercise 6–7 days a week1.7253,032
Extra active: physical job plus hard training1.93,340

Step-by-step solution

  1. Change your height to centimeters, because the formula uses metric units (1 in is exactly 2.54 cm)

    (5×12+10)×2.54=177.8 cm

  2. Change your weight to kilograms (1 lb is exactly 0.45359237 kg)

    180 lb×0.453592=81.647 kg

  3. Use the Mifflin-St Jeor formula for a male. It uses your weight in kg, height in cm and age in years

    BMR=10×W + 6.25×H − 5×A + 5

  4. Put your measurements into the formula

    10×81.647+6.25×177.8−5×35+5=1,757.7 kcal/day

  5. Divide by 24 to see what you burn each hour at rest

    1,757.724=73.2 kcal/hour

  6. Check it with a second formula, Harris-Benedict, using the same numbers

    Harris-Benedict=1,836.7 kcal/day

  7. Find your daily needs: multiply your BMR by an activity factor, from 1.2 if you sit most of the day to 1.9 if you are very active

    1,757.7×1.2=2,109 … 1,757.7×1.9=3,340

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

Please note: This calculator gives a general screening estimate, not a diagnosis. Talk to a qualified healthcare professional about your individual health.

What this calculator does

Find out how many calories your body burns in a day while you rest. That number is your basal metabolic rate, or BMR. It's the energy you use just to stay alive: breathing, pumping blood, keeping warm and keeping your organs working. For most people it's the biggest part of the calories they burn each day. So it's the best place to start when you want to know how much to eat.

Measuring BMR properly takes lab equipment, so most people use a formula instead. You can pick from three well-known ones, and the calculator checks your answer against a second one. It also shows how many calories you'd need each day at different activity levels. The result is an estimate for a typical adult with your measurements. It isn't a measurement of your own body, and it isn't a diagnosis. If you're planning big changes to how you eat, talk to a doctor or a registered dietitian.

Where it's used

Why this math matters outside the classroom:

  • Evaluating a formula. Students substitute 70 kg, 175 cm and age 30 into Mifflin-St Jeor for a man: 700 + 1,093.75 − 150 + 5 = 1,648.75 kcal.
  • Unit conversion. Converting 154 lb to about 69.9 kg and 5 ft 10 in to 177.8 cm comes first, since the equations use metric units.
  • Meal planning. People planning a week of meals start from a BMR estimate and multiply it by an activity factor to set a daily calorie budget.
  • Comparing equations. Nutrition students run the same person through Mifflin-St Jeor and Harris-Benedict to see how far two published equations disagree.
  • Fitness tracking. Fitness apps re-estimate BMR whenever someone logs a new weight, so daily calorie figures follow the change.

Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.EE.A.2.c, 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Choose a formula. Mifflin-St Jeor is the default. Katch-McArdle also needs your body fat percentage.
  2. Pick US or metric units. Then enter your sex, age, height and weight.
  3. Read your estimated BMR in kilocalories per day, plus the same rate per hour. Kilocalories (kcal) are the 'calories' you see on food labels.
  4. Use the activity table to see roughly how many calories you need each day. The calorie (TDEE) calculator adds targets for losing or gaining weight.

What the inputs mean

Equation
Mifflin-St Jeor and Harris-Benedict use your sex, age, height and weight. Katch-McArdle skips sex and age. It works from your lean body mass instead, which is everything in your body that isn't fat. That can suit you if you know your body fat percentage fairly well.
Sex
Each formula was built separately from data on men and on women, so the numbers in it differ by sex.
Age
Enter whole years. All three formulas were built from data on adults.
Body fat
Only Katch-McArdle uses this. An estimate from the body fat calculator, a scale or a professional check is fine. Keep in mind the BMR can only be as good as this number.

Formula and method

Mifflin-St Jeor (male)   = 10 × W + 6.25 × H − 5 × A + 5
Mifflin-St Jeor (female) = 10 × W + 6.25 × H − 5 × A − 161
Harris-Benedict 1984 (male)   = 88.362 + 13.397 × W + 4.799 × H − 5.677 × A
Harris-Benedict 1984 (female) = 447.593 + 9.247 × W + 3.098 × H − 4.330 × A
Katch-McArdle = 370 + 21.6 × LBM,  LBM = W × (1 − body fat % ÷ 100)
Daily calories = BMR × activity factor   (1.2, 1.375, 1.55, 1.725 or 1.9)

In the formulas, W is your weight in kilograms, H is your height in centimeters and A is your age in years. LBM is your lean body mass in kilograms: your weight minus the part that is fat. The answers are in kilocalories per day. If you enter US units, the calculator converts them exactly first: 1 inch = 2.54 cm and 1 pound = 0.45359237 kg.

Mifflin-St Jeor was published in 1990. It came from measuring healthy adults, some of normal weight and some with obesity. Harris-Benedict dates from 1919. The version here is the 1984 update by Roza and Shizgal, who added newer measurements to the original data. Katch-McArdle starts from lean mass, because the parts of you that aren't fat burn most of your resting energy.

The activity factor is a number between 1.2 and 1.9. Multiplying your BMR by it gives a rough count of the calories you burn on a typical day, including movement.

Worked example

A 35-year-old man is 5 ft 10 in tall and weighs 180 lb. He uses the default Mifflin-St Jeor formula.

  1. Height: (5 × 12 + 10) × 2.54 = 177.8 cm.
  2. Weight: 180 × 0.45359237 = 81.647 kg.
  3. BMR = 10 × 81.647 + 6.25 × 177.8 − 5 × 35 + 5 = 816.47 + 1,111.25 − 175 + 5 = 1,757.7 kcal/day.
  4. Per hour: 1,757.7 ÷ 24 = 73.2 kcal/hour.
  5. To compare, the updated Harris-Benedict formula gives 88.362 + 13.397 × 81.647 + 4.799 × 177.8 − 5.677 × 35 = 1,836.7 kcal/day.
  6. Activity table: about 2,109 kcal/day if he sits most of the day, 2,417 lightly active, 2,724 moderately active, 3,032 very active and 3,340 extra active.

Result: His estimated BMR is about 1,758 kcal per day (Harris-Benedict says about 1,837). If he's lightly active, he needs about 2,417 kcal per day.

Understanding the result

BMR is what you'd burn lying still all day. In real life you burn more, because moving, working, exercising and even digesting food all add to it. That's why BMR on its own shouldn't be your daily eating target.

The three formulas often differ by 50 to 150 kcal a day for the same person. Don't let that worry you. It's an honest picture of the uncertainty. These formulas describe averages, and two people with the same measurements can burn noticeably different amounts.

The activity table multiplies your BMR by the standard factors used with these formulas. Each factor covers a broad range of people. So treat the daily numbers as a starting point, then adjust based on what your weight actually does.

If you know your body fat percentage fairly well, Katch-McArdle is a useful second check. This matters most for very muscular people, because the weight-based formulas tend to guess too low for them.

Assumptions and limitations

  • You're an adult whose body is in a steady state. That means not ill, pregnant or breastfeeding, and not coming off a stretch of very strict dieting.
  • Your measurements are accurate. For Katch-McArdle, your body fat percentage is a reasonable estimate.
  • Nothing is rounded during the math. The BMR you see is rounded to the nearest kilocalorie.
  • These formulas give averages for groups of people. Your own BMR can differ from all of them, sometimes by 10% or more.
  • The formulas were built from groups of adults in the United States. They may be less accurate for groups that weren't in that data. The same goes for older adults, and for people who are very light, very heavy or very muscular.
  • They don't account for health conditions, medicines or hormone changes that affect how fast you burn energy. Only a clinical test, such as indirect calorimetry (measuring the air you breathe in and out), measures your actual rate.
  • This tool isn't suitable for children or teens.

Frequently asked questions

Which BMR formula should I use?

Mifflin-St Jeor is the one most often recommended for adults. It was built from more recent data, and it has generally matched measured values well. Use Katch-McArdle if you have a body fat estimate you trust. Treat the updated Harris-Benedict result as a second opinion.

What is a normal BMR?

There's no single normal number, because BMR depends on your size, sex and age. With Mifflin-St Jeor, a 35-year-old man who is 5 ft 10 in and 180 lb comes out at about 1,758 kcal a day. A 35-year-old woman who is 5 ft 4 in and 150 lb comes out at about 1,360 kcal a day. Your result is an estimate for an average person with your measurements.

Is BMR the same as resting metabolic rate?

They're close, but not quite the same. BMR is measured under stricter conditions: fully rested, without eating, and lying down. Resting metabolic rate is usually a little higher. In everyday use, people often treat the two as the same thing, and these formulas work for either one.

How many calories should I eat?

BMR is only what you burn at rest. To estimate your total daily needs, multiply it by an activity factor, which is what the TDEE calculator does. For advice that fits you, especially about losing or gaining weight, talk to a healthcare professional or registered dietitian.

Why does my BMR go down as I get older?

Mifflin-St Jeor and Harris-Benedict include age because, on average, older adults in the studies burned less energy at rest. Part of that came from changes in lean mass. The formula applies that average trend to everyone.

Are my measurements stored or shared?

No. The math runs in your own browser, and this calculator doesn't make a shareable link with your measurements in it.

How this calculator is checked

Method: Mifflin MD, St Jeor ST et al. (1990) predictive equation; Harris-Benedict equation as revised by Roza AM and Shizgal HM (1984); Katch-McArdle lean-mass equation (370 + 21.6 × LBM); conventional activity factors 1.2–1.9 for the daily-calorie table. Unit conversions use the international inch and pound. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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