Fat-Free Mass Index (FFMI)
Lean body mass relative to height — the metric that tells you whether you carry muscle or just weight, and whether a “high BMI” is real muscle.
Formula
FFMI = lean mass (kg) ÷ height (m)²
Healthy range
Men: 18–21 average, 22–24 muscular, 25+ near the natural limit · Women: roughly 15–18 average.
Military & first-responder angle
The muscular soldier who fails a weight table but passes WHtR is exactly the person FFMI explains. The 540 ACFT exemption protects the same high-muscle cohort.
Calculator
Fat-Free Mass Index normalizes lean mass to height — a physique/readiness reference, not a pass/fail line.
Result
Quick answers
Related metrics
WHtR
Waist circumference divided by height — the metric the U.S. military adopted as its joint-force body-compositi…
Read →Body fat %
The percentage of your weight that is fat. The U.S. Navy circumference method estimates it from height, neck, …
Read →BMI
Weight divided by height squared. Still used for general screening and in some enlistment height-weight tables…
Read →WHR
Waist divided by hip circumference — a classic central-obesity index that predates WHtR. The military uses WHt…
Read →BMR
The calories your body burns at rest. The Mifflin–St Jeor equation is the most accurate formula for most adult…
Read →TDEE
BMR multiplied by an activity factor — the calories you burn per day including training. The number to use whe…
Read →LBM
Your total weight minus fat — muscle, bone, organs, and water. Used to set protein targets and evaluate compos…
Read →Ideal weight
Devine, Robinson, Miller, and Hamwi formula estimates of a healthy weight for your height — planning reference…
Read →Water intake
Evidence-based hydration targets for your weight and activity — especially relevant to accurate weigh-ins and …
Read →