Katch-McArdle BMR Calculator

Katch-McArdle ignores height and total weight and works from lean body mass alone. Enter your weight and body-fat percentage — or, if you know it, your lean body mass directly.

The Katch-McArdle formula

It uses one number — lean body mass (LBM), your weight minus your fat mass:

BMR = 370 + (21.6 × LBM in kg)
LBM = weight × (1 − body-fat% ÷ 100)

Worked example

Someone weighing 80 kg at 20% body fat has 80 × (1 − 0.20) = 64 kg of lean mass. BMR = 370 + (21.6 × 64) = 370 + 1,382 = 1,752 calories/day. Drop to 12% body fat at the same weight and LBM rises to 70.4 kg, lifting BMR to about 1,891 — the formula rewards a leaner composition.

When to use Katch-McArdle instead of Mifflin-St Jeor

Use Katch-McArdle when you have a trustworthy body-fat measurement and your build is far from average — lean and muscular, or carrying a lot of fat. Because it scales with lean mass, it gives a muscular person a higher, more realistic number than height/weight equations, and someone with high body fat a lower one. Without a good body-fat figure, Mifflin-St Jeor is the safer choice.

From BMR to a calorie target

BMR is not a target — nobody lies still all day. Multiply it by an activity factor with the TDEE calculatorto get maintenance calories, adjust up or down for a goal with the calorie calculator, then split the target with the macro calculator. For the body-fat input this page can use, see the body fat calculator.

The other BMR equations

Mifflin-St Jeor — the modern default, and the parent calculator.
Harris-Benedict — The classic 1919 equation, revised 1984. Same inputs as Mifflin but reads about 5% higher.

Source: Katch & McArdle.

Related calculators

Related guides

Frequently asked questions

When is Katch-McArdle the best choice?

When you have a reliable body-fat measurement and your body composition is far from average — very lean, very muscular, or both. Because it scales BMR with lean mass rather than total weight, it does not penalise a muscular person the way height/weight equations can, or over-estimate for someone carrying a lot of fat (fat tissue burns far less at rest than muscle).

Where do I get my body-fat percentage?

A DEXA scan is the most accurate; a careful 7-site skinfold with calipers is a good free alternative. The U.S. Navy tape method and bioimpedance scales are more approximate. Whatever you use, an error of a few points in body fat moves the BMR estimate by only 20 to 40 calories, so it is fairly forgiving.

How is lean body mass calculated here?

Lean mass = weight × (1 − body-fat% ÷ 100). For example, 80 kg at 20% body fat is 64 kg of lean mass. If you enter a lean-body-mass figure directly, that is used as-is and the body-fat field is ignored.

Why no height or age input?

The formula does not use them. Lean body mass already captures most of what height and age contribute to resting metabolism (taller and younger people tend to have more of it). That is also the limitation — two people with the same lean mass get the same estimate regardless of age.

How does it compare to Mifflin-St Jeor?

For someone with an average body-fat percentage the two land within a few percent of each other. They diverge for outliers: a lean, muscular athlete will usually get a higher, more realistic figure from Katch-McArdle, while someone with a high body-fat percentage will get a lower one.

What if I don't know my body fat?

Use the Mifflin-St Jeor equation on the main BMR calculator instead — it needs only age, sex, height and weight. Come back to Katch-McArdle once you have a body-fat measurement you trust.

Last reviewed: September 2026. Figures and formulas are checked against their published sources; see the site's data notes.