Find your basal metabolic rate with three proven equations
Your basal metabolic rate (BMR) is the energy your body uses to stay alive at complete rest — breathing, pumping blood, keeping warm, repairing cells and running your brain. For most people it is the single biggest part of daily calorie burn. This BMR calculator estimates it with the three equations dietitians and coaches use most, side by side, so you can see how much they agree.
Enter your age, sex, height and weight in metric or imperial units. Add your body fat percentage if you know it to unlock the Katch-McArdle formula. Results appear instantly in kilocalories and kilojoules, along with your daily needs at five activity levels.
All three formulas are population averages: your true BMR can differ by 10% or more. Treat the result as an estimate for healthy adults, not medical advice, and speak to a doctor or registered dietitian if you have a medical condition.
How to use the BMR Calculator
- Choose metric or imperial units and select male or female.
- Enter your age, height and weight. The example values show a typical adult so you can see the layout first.
- Optionally enter your body fat percentage — from a DEXA scan, smart scale or the body fat calculator.
- Pick which formula to show in the main result. Mifflin-St Jeor is selected by default.
- Compare the three estimates and read the activity table to see your total daily calorie needs.
BMR Calculator features
Three equations at once
Mifflin-St Jeor, revised Harris-Benedict and Katch-McArdle are calculated together so differences are obvious.
kcal and kJ
Every figure is shown in kilocalories and kilojoules (1 kcal = 4.184 kJ), useful in Australia, New Zealand and Europe where labels use kJ.
Activity table
Your BMR multiplied by the standard activity factors from 1.2 to 1.9 gives daily needs from desk-bound to extra active.
Metric or imperial
Switch between cm/kg and ft/in/lb; your numbers convert automatically and your choice is remembered.
Lean-mass option
Katch-McArdle uses lean body mass, which suits muscular people whom weight-based formulas can underestimate.
The BMR formulas explained
W is weight in kilograms, H is height in centimetres and A is age in years. The calculator converts imperial entries to these units first.
- Mifflin-St Jeor (1990): men 10W + 6.25H − 5A + 5; women 10W + 6.25H − 5A − 161. Developed from 498 healthy adults, it is the equation the Academy of Nutrition and Dietetics recommends for healthy people, and a 2005 systematic review found it the most accurate of the common formulas.
- Revised Harris-Benedict (Roza and Shizgal, 1984): men 88.362 + 13.397W + 4.799H − 5.677A; women 447.593 + 9.247W + 3.098H − 4.330A. The original 1919 version tends to overestimate modern adults by a few per cent.
- Katch-McArdle: 370 + 21.6 × lean body mass (kg), where lean mass = weight × (1 − body fat % ÷ 100). It ignores age and sex because lean tissue drives most of your resting burn.
Worked example
A 30-year-old man who is 180 cm tall and weighs 80 kg: Mifflin-St Jeor gives 800 + 1,125 − 150 + 5 = 1,780 kcal/day (about 7,448 kJ). Harris-Benedict gives about 1,854 kcal. If he has 18% body fat, his lean mass is 65.6 kg and Katch-McArdle gives 370 + 21.6 × 65.6 = 1,787 kcal.
Multiply by an activity factor to get total daily energy expenditure (TDEE). At “moderately active” (× 1.55) he needs about 2,759 kcal to maintain his weight — the calorie calculator takes this further with weight-loss and gain targets.
BMR, RMR and TDEE — what’s the difference?
BMR is measured under strict lab conditions: after an overnight fast, lying still in a warm room. Resting metabolic rate (RMR) uses looser conditions and is usually slightly higher. The equations above estimate either, and in everyday use the terms are interchangeable.
TDEE adds digesting food (about 10% of intake) and all movement, from walking to workouts. BMR typically makes up 60–70% of TDEE for people who don’t exercise much. Building muscle nudges BMR up; ageing, crash dieting and losing lean mass push it down.
BMR Calculator FAQ
Which BMR formula is most accurate?
For most healthy adults, Mifflin-St Jeor is the most reliable of the common equations and predicts measured resting metabolism within about 10% for most people. If you know your body fat percentage and are lean or muscular, Katch-McArdle can be closer.
Should I eat my BMR calories to lose weight?
Not usually. BMR is what you burn lying still all day; your real needs are higher once you move. Eating well below your TDEE, rather than at BMR, is the usual approach — and very low intakes should only be followed with medical supervision.
Why does my BMR go down as I get older?
All three weight-based equations subtract calories for each year of age, reflecting the gradual loss of muscle and organ mass. Strength training helps protect lean mass and slows the decline.
Why is my BMR lower than my friend’s?
BMR scales with body size and lean mass. Taller, heavier and more muscular people burn more at rest, and men generally have higher BMR than women of the same size because they carry more lean tissue.
How can I measure my body fat for Katch-McArdle?
DEXA scans and underwater weighing are the most accurate. A tape-measure estimate with the body fat calculator or a bioimpedance scale is good enough for a sensible Katch-McArdle result.
Does this BMR calculator store my data?
No. All calculations happen in your browser. Only your metric or imperial preference is saved on your own device.