BMR / RMR Calculator
Estimate basal or resting metabolic rate from four equations, compare their spread, and see why BMR is not a calorie target. Browser-only.
Results
What this BMR calculator estimates
This calculator estimates the energy your body uses at rest. The important detail is the label: some equations predict basal metabolic rate and some predict resting metabolic rate. The result says which one you are seeing instead of handing over one unlabelled BMR/RMR number.
It does not calculate activity, total daily energy expenditure, calorie deficits, weight-loss targets or macronutrients. Those belong to the calorie and TDEE tools, because an intake target needs safeguards this calculator is not applying.
How to calculate basal metabolic rate
Calculating basal metabolic rate means putting height, weight, age and sex through a published equation. This basal metabolic rate calculator uses Mifflin-St Jeor by default, in the full-precision coefficients the original paper published: 9.99 times weight in kilograms, plus 6.25 times height in centimetres, minus 4.92 times age in years, then plus 5 for men or minus 161 for women.
Worked through, a man of 75 kg and 175 cm aged 30 gives 749.25 plus 1093.75 minus 147.6 plus 5, which is about 1,700 kcal a day. The same measurements read against the female constant give about 1,534. Many tools round the coefficients to 10, 6.25 and 5 before calculating; that is a different equation, and this calculator does not use it.
Revised Harris-Benedict is the equation here that predicts a basal rather than a resting rate. For men it is 88.362 plus 13.397 times weight in kilograms, plus 4.799 times height in centimetres, minus 5.677 times age in years. Katch-McArdle and Cunningham work from fat-free mass instead, at 370 plus 21.6 times lean kilograms and 500 plus 22 times lean kilograms, which is why they appear only once you enter a body fat percentage.
Whichever phrase brought you here - base metabolism calculator, metabolic rate calculator, BMR calculator - the arithmetic is the one above. The distinction that changes the answer is basal against resting, and the table below states which of the two each equation was published to predict.
Equations compared
Every supported equation your inputs allow is shown. If you enter body fat, the two lean-body-mass equations are added to the comparison. The equations are not averaged.
| Equation | Quantity | Inputs |
|---|---|---|
| Mifflin-St Jeor | Resting metabolic rate | Height, weight, age and sex |
| Revised Harris-Benedict | Basal metabolic rate | Height, weight, age and sex |
| Katch-McArdle | Resting metabolic rate | Lean body mass from body fat percentage |
| Cunningham | Resting metabolic rate | Lean body mass from body fat percentage |
This is not a calorie target
A resting-rate estimate is the energy used at rest. It is not what you should eat. Eating to a resting-rate number can be unsafe, especially when a person's actual daily expenditure is higher or when a low target would need clinical supervision.
Use the calorie calculator when you want an intake estimate. It adds activity, applies the selected goal and refuses to deliver targets below the published minimum intake floor. That page runs the same Mifflin-St Jeor equation as its default, so a Mifflin-St Jeor calorie calculator and this resting-rate estimate share a starting point and part company at the activity multiplier.
Limits and sources
This is an educational estimate for healthy adults aged 18 to 80. It is not suitable during pregnancy or breastfeeding, for children or adolescents, or for anyone managing an eating disorder, thyroid disorder, medication effect or medical condition that changes metabolism.
Sources include Mifflin-St Jeor 1990, Roza and Shizgal 1984, Harris and Benedict 1918, Cunningham 1980 and 1991, Cleveland Clinic basal metabolic rate guidance, and AUDIT-HEALTH-04. Sources reviewed 27 August 2026.
Frequently asked questions
Is BMR the same as RMR?
Not exactly. Basal metabolic rate is measured under stricter lab conditions after full rest and fasting. Resting metabolic rate is measured after a shorter rest and is usually a little higher. This calculator labels which quantity each equation predicts instead of converting one into the other.
Which BMR equation should I choose?
Mifflin-St Jeor is the default for most adults because it uses common measurements and is widely used for resting energy estimates. Katch-McArdle and Cunningham can be useful when you have a reliable body fat estimate. Revised Harris-Benedict is shown for comparison and is labelled as basal.
Should I eat my BMR?
No. BMR or RMR is what your body uses at rest, not a food target. A calorie target needs activity, goal direction and a safety floor. This calculator deliberately does not apply those because it is not estimating intake.
Why do the equations disagree?
They were derived from different data and some predict different quantities. The comparison table shows the spread instead of averaging it, because an average can hide the fact that the methods are not all measuring exactly the same thing.
Is this the same as a metabolic rate calculator?
Yes. Metabolic rate calculator, base metabolism calculator and resting metabolic rate calculator all describe a tool of this kind. The distinction worth keeping is between basal rate and resting rate, which the comparison table states per equation rather than leaving it to the name of the page.
Can I use this during pregnancy or breastfeeding?
No. Pregnancy and breastfeeding change energy needs in ways this calculator does not model. It is also not intended for children, adolescents, eating-disorder management, thyroid disorders, medication effects or clinical nutrition planning.