The formula
How to calculate resting metabolic rate
Resting metabolic rate is the energy used at rest under everyday rather than laboratory conditions. It runs about 10% above basal metabolic rate, because the measurement does not require an overnight fast and complete stillness.
This page uses the revised Harris-Benedict equation, the older of the two standard formulas. Showing Mifflin-St Jeor alongside makes the disagreement visible — they typically differ by 50 to 150 kcal a day.
The calculator asks for:
- Weight (kg)
- Height (cm)
- Age (years)
No submit button: type and the answer moves. Your inputs end up in the link, so the page can be shared already filled in.
None of the fields above need specialist equipment to fill in — the inputs are the kind of measurements that can be taken at home with a tape measure or scale, which is exactly why this style of calculation is widely used as a first, approximate check rather than a diagnostic one.
Why resting metabolic rate matters
People usually look up a resting metabolic rate calculation to put a number on something they can already sense but cannot quite quantify — how their fitness compares with a reference range, how a measurement is trending, or what a change actually means. A calculator turns that vague sense into a concrete figure, which is useful even though the figure itself is only ever an estimate.
Because the calculation depends on a formula rather than a device, it is useful anywhere a scale, a tape measure or a stopwatch is available, without needing specialist equipment — which is also exactly why it should be treated as an estimate rather than a clinical measurement.
None of the figures produced on this page are intended to replace a proper assessment, and nothing here should be read as a diagnosis or a treatment recommendation. What a calculator like this is good for is preparation — arriving at an appointment with an actual number already in hand, rather than a vague sense of a change, tends to make that conversation more useful for everyone involved.
Where a result depends on more than one measurement, small errors in each input tend to compound rather than cancel out — a slightly mismeasured waist and a slightly mismeasured height, taken together, can shift a derived figure more than either error would on its own. Taking each measurement carefully, and ideally twice, is worth the extra minute it takes.
Worked example
A concrete run-through, using the values already in the fields:
- Weight: 75 kg
- Height: 175 cm
- Age: 35 years
That gives:
- RMR, male equation: 1,734 kcal/day
- RMR, female equation: 1,532 kcal/day
- Mifflin-St Jeor for comparison, male: 1,674 kcal/day
Those starting figures exist only to show the calculation working, not as a target or a reference value to compare yourself against — replace them with your own measurements in the calculator above and the same formula applies exactly as shown.
Reading the result
Where they differ, most dietitians favour Mifflin-St Jeor, which validated better against measured values in modern populations. Harris-Benedict tends to run high, particularly for people carrying more weight.
Where this goes wrong. Neither equation accounts for body composition, thyroid function or medication, all of which move the real figure. Use it as an estimate to adjust from, not a target — and take clinical questions to a professional.
As with any general-purpose formula, the result here is an estimate derived from population averages, not a measurement specific to you — a reasonable starting point for a conversation with a qualified professional, not a replacement for one. Nothing on this page is medical advice.
Not quite. BMR is measured under strict fasted, fully rested conditions; RMR under ordinary resting conditions, which produces a figure roughly 10% higher. In everyday use the terms are often swapped.
Mifflin-St Jeor for most purposes — it is more accurate across modern populations. Harris-Benedict remains in wide use because it predates it and is embedded in a lot of software.
The answer it gives you is rMR, male equation. With 75 kg weight, 175 cm height and 35 years age, that comes to 1,734 kcal/day. Change any field and the figure moves with it.
It uses a published formula applied exactly as defined, so the arithmetic itself is precise — but the formula is a population-level estimate, and individual results can vary from it for reasons the formula has no way to account for. Treat the output as a reasonable estimate rather than a measured or diagnostic value.
For most people, yes — a single reading is a snapshot, while the same measurement repeated consistently over weeks or months shows a trend, which is generally more informative than any one figure taken in isolation.
Small differences between calculators usually come down to which published formula or reference dataset each one uses — several equations in this area exist in more than one accepted version. This page states the specific formula used in the section above, so it is possible to check directly whether another source is using the same one.