Basal Metabolic Rate Calculator (Katch-McArdle)
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
The Katch-McArdle formula calculates basal metabolic rate with BMR = 370 + 21.6 × lean mass (kg). For a weight of 80 kg with 20% body fat (i.e. 64 kg of lean mass), the estimated BMR is 1,752 kcal/day.
Explanation
The Katch-McArdle formula estimates basal metabolic rate (the energy spent at strict rest, to maintain the body's vital functions) from lean mass rather than total weight — unlike our calorie needs calculator, which uses the Mifflin-St Jeor formula based on weight, height, age, and sex, with no need for a body composition measurement. Lean mass (total weight minus fat mass) covers the metabolically active tissues of the body, mainly muscle, which burns noticeably more energy at rest than fat tissue. That's why Katch-McArdle is often considered more accurate for people whose body composition departs from the statistical average used by weight-only formulas: a very muscular athlete, for example, generally has a higher basal metabolic rate than someone of the same weight but with more fat mass, a nuance Katch-McArdle captures directly, unlike formulas that only consider total weight. This added accuracy comes at a cost, though: it requires knowing your body fat percentage (see our body fat calculator to estimate it), a figure that itself carries a margin of error depending on the method used (bioelectrical impedance, skinfold calipers, DEXA, the most accurate but least accessible). An imprecise body composition estimate going in will therefore give an equally imprecise BMR coming out, however rigorous the formula itself is.
Example: 80 kg, 20% body fat
Inputs
Weight: 80 kg. Body fat percentage: 20%.
Calculation
Lean mass = 80 × (1 − 0.20) = 64 kg. BMR = 370 + 21.6 × 64 = 370 + 1,382.4 = 1,752.4 kcal/day.
Result
The estimated basal metabolic rate for this profile is about 1,752 kcal per day.
Frequently asked questions
Why choose Katch-McArdle over the Mifflin-St Jeor formula?
Katch-McArdle becomes more useful when body composition noticeably departs from the statistical average (very muscular people or those with very low body fat), since it directly accounts for lean mass rather than total weight alone. For someone with body composition closer to average, both formulas generally give fairly close results, and Mifflin-St Jeor stays simpler to use since it requires no body composition measurement.
What happens if my body fat percentage estimate is inaccurate?
The BMR result will be less reliable the less accurate the starting estimate is, since the formula relies entirely on the lean mass calculated from that percentage. Body composition measurement methods have varying margins of error (a consumer bioelectrical impedance scale can differ by several percentage points from a more accurate DEXA measurement): keep this uncertainty in mind when interpreting the result.
Does the BMR obtained equal the total calories to eat per day?
No, BMR only represents energy expenditure at strict rest, with no physical activity at all. Total daily calorie needs are higher, accounting for physical activity level (see our calorie needs calculator for that adjustment factor): BMR alone should never be used directly as a daily calorie target.