Unlike height/weight formulas, Katch-McArdle works from your lean body mass. If you know your body-fat percentage, it can be the most accurate BMR estimate available.
Katch-McArdle estimates BMR from lean body mass alone:
Because it's driven by lean mass rather than total weight, Katch-McArdle is more accurate for people whose body composition differs from average — lean, muscular individuals, or those with higher body fat — provided the body-fat input is reliable.4 Its weakness is exactly that dependency: a guessed body-fat percentage produces a guessed BMR. If you don't have a measured value, Mifflin-St Jeor is the safer default.3
To use it here, pick Katch-McArdle in the formula dropdown and enter your body-fat percentage. See the methodology & sources page for references.
Measured methods (DEXA, calipers, bioimpedance scales) vary in accuracy. Use the most reliable figure you have; a rough guess undermines the formula's advantage.
Only when the body-fat input is accurate. With a reliable measurement it can beat Mifflin-St Jeor, especially for very lean or muscular people. Without one, use Mifflin-St Jeor.