The three BMR equations
With weight W in kilograms, height H in centimeters and age A in years:
| Equation | Formula (calories/day) |
|---|---|
| Mifflin-St Jeor, men | 10W + 6.25H − 5A + 5 |
| Mifflin-St Jeor, women | 10W + 6.25H − 5A − 161 |
| Revised Harris-Benedict, men | 13.397W + 4.799H − 5.677A + 88.362 |
| Revised Harris-Benedict, women | 9.247W + 3.098H − 4.330A + 447.593 |
| Katch-McArdle, anyone | 370 + 21.6 × lean body mass (kg) |
Lean body mass is weight × (1 − body-fat % ÷ 100). The calculator converts pounds and feet to metric for you. Full citations are on the methodology page.
From BMR to daily calories
For most adults BMR is the largest single part of the calories burned in a day; the rest comes from digesting food and from movement. To estimate daily needs, BMR is multiplied by an activity factor between 1.2 and 1.9. With the example above (BMR 1,370), a sedentary day comes to about 1,644 calories. The table of activity levels in the calculator shows every level at once. For the difference in more detail, read BMR vs TDEE.
What raises or lowers BMR
- Size: more body tissue to maintain means a higher BMR.
- Muscle: lean tissue uses more energy than fat tissue, which is why Katch-McArdle works from lean mass.
- Age: BMR tends to decline gradually through adulthood, partly because of changes in body composition.
- Sex: men average higher BMRs than women of the same height and weight, mainly due to differences in body composition.
- Other factors such as thyroid function, illness, some medications, and pregnancy can change BMR in ways a formula can’t see. If you suspect one of these, talk to a doctor.
Frequently asked questions
What is BMR?
Basal metabolic rate is the energy your body uses in a day at complete rest: breathing, circulation, keeping organs working and maintaining body temperature. It does not include digestion, daily movement or exercise.
What is a normal BMR?
There isn’t one “normal” number because BMR scales with body size, age and sex. As a rough idea, the Mifflin-St Jeor equation gives a 30-year-old woman who is 165 cm and 65 kg a BMR of about 1,370 calories. Larger, younger and more muscular people sit higher.
Should I eat my BMR?
BMR is not an eating target. It is the energy used before any movement at all, so almost everyone burns more than their BMR. Daily needs are closer to your TDEE, shown as the second number here. Eating well below your needs for long periods is not recommended without medical guidance.
Why do the three formulas give different answers?
They were built from different groups of people measured in different decades. Mifflin-St Jeor (1990) is the usual default; revised Harris-Benedict (1984) tends to come out a little higher; Katch-McArdle uses lean body mass and depends on an accurate body-fat estimate.
Can I measure my BMR directly?
Yes, with indirect calorimetry, which measures oxygen use and carbon dioxide output. Some clinics, hospitals and sports labs offer it. Calculators like this one estimate the same thing from body measurements.