BMR Calculator
Calculate your basal metabolic rate with three formulas side by side — Mifflin-St Jeor, Harris-Benedict and Katch-McArdle — in metric or imperial units. See why they disagree and which one fits you.
Also available as a desktop app for Windows.
About this tool
Your basal metabolic rate (BMR) is the energy your body spends keeping itself alive at complete rest — breathing, circulating blood, keeping warm — before any activity, digestion or exercise is added on top. Almost every calorie target starts from this number.
There is no single BMR formula. This tool shows three side by side: Mifflin-St Jeor, the current general-purpose recommendation; Harris-Benedict, the classic formula most older charts and plans were built on; and Katch-McArdle, which uses your lean body mass and is the most personal of the three when you actually know your body fat percentage.
They will not agree exactly — a spread of 100–200 kcal/day between formulas is normal, because each was fitted to a different population. Seeing all three at once is the point: it turns a single reassuring number into an honest range. Everything runs locally in your browser.
Frequently asked questions
- Which formula should I trust?
- For most people, Mifflin-St Jeor — it is the current general recommendation and tested most accurately against measured values. Harris-Benedict tends to read slightly higher for the same person. If you reliably know your body fat percentage, Katch-McArdle is worth taking seriously, because it is driven by lean body mass rather than total weight.
- Why do the three numbers differ?
- Each formula was fitted to a different study population at a different time, and each weighs age, height, weight and (for Katch-McArdle) lean mass differently. They are all estimates of the same quantity, so disagreement between them is information: it shows roughly how precise any single one can be.
- Is BMR the same as the calories I burn in a day?
- No — BMR is only the resting part. Total daily burn is BMR multiplied by an activity factor (typically 1.2–1.9). That is what a TDEE calculator does; start from the Mifflin-St Jeor value here if you want one number to take forward.
- Does it work in pounds and feet?
- Yes — switch the unit selector to imperial and enter height in feet + inches and weight in pounds. The conversion is done at full precision internally (1 lb = 0.45359237 kg), not rounded first, so results match the metric input.
- Why does Katch-McArdle ignore my age?
- It does not use age, height or sex at all — only lean body mass: 370 + 21.6 × LBM (kg). Muscle tissue is the dominant driver of resting burn, so when body composition is known the other variables add little. That is also its weakness: the result is only as good as the body fat figure you feed it.