Skip to main content
Calculator Answers

FFMI Calculator

Source: Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med. 1995;5(4):223-228 · Source verified August 22, 2026

Blake Boege
Written by Blake Boege · Founder, Calculator Answers

An FFMI calculator is a body composition tool used to compute the Fat-Free Mass Index, which measures a person's muscle mass relative to their height. Unlike the standard Body Mass Index (BMI), FFMI distinguishes between fat tissue and muscle mass, making it a more accurate metric for athletes and bodybuilders. It calculates FFMI by dividing fat-free mass in kilograms by height in meters squared, and it can also apply a normalization adjustment for tall individuals. Fitness coaches, bodybuilders, and health researchers use this calculator to track muscle growth, set realistic physical goals, and evaluate body composition health.

Pick imperial or metric, choose a sex for the reference bands, and enter height, weight, and body fat percentage. The calculator returns fat-free mass, raw FFMI, height-normalized FFMI, and a reference category band.

Quick Answer

Calculate your Fat-Free Mass Index (FFMI) to measure muscle density. Enter your weight, height, and body fat percentage to see your category.

Units
Sex (for category bands)
in

e.g. 70

lb

e.g. 180

%

Use a method you trust: DEXA, BodPod, calipers, or a careful Navy-tape estimate. · e.g. 15

About FFMI

FFMI is a rough screen for how much muscle a person carries relative to their height. The normalized version (Kouri 1995) corrects for height so taller and shorter lifters can be compared. Category bands are reference points, not strict cutoffs.

Educational estimate only. Not a medical, fitness, or anti-doping conclusion. Body fat input drives most of the error; use the most accurate method you have.

FFMI

Normalized FFMI

22.09

Excellent / advanced natural lifter

Body weight81.65 kg
Height1.778 m
Body fat15%
Fat mass12.25 kg
Fat-free mass69.4 kg
FFMI (raw)21.95
Normalized FFMI22.09

FFMI = fat-free mass (kg) divided by height (m) squared. Normalized FFMI adds 6.1 × (1.8 − height in meters) so lifters of different heights can be compared on the same scale.

Was this helpful?

Examples

180 lb · 70 in · 15% BF · male

FFM ~69.5 kg · FFMI ~21.9 · normalized ~22.0

82 kg · 178 cm · 15% BF · male

FFM ~69.7 kg · FFMI ~22.0

140 lb · 65 in · 22% BF · female

FFM ~49.5 kg · FFMI ~17.7 · normalized ~18.6

200 lb · 73 in · 10% BF · male

FFM ~81.6 kg · FFMI ~23.3

How it works

FFMI swaps total body weight for fat-free mass in the BMI formula. Normalized FFMI adds a height correction so the metric scales fairly across short and tall lifters.

Fat-free mass · FFM = weight × (1 − bodyfat%/100)

FFMI · FFMI = FFM_kg / height_m²

Normalized FFMI · FFMI + 6.1 × (1.8 − height_m)

One divergence worth naming, because this page cites Kouri for the ceiling of 25 and then measures you against it on a slightly different scale. Kouri published the correction as 6.3 × (1.80 m − height); this calculator uses 6.1, which is the variant in common circulation. The two differ by at most 0.08 FFMI points across heights from 1.40 m to 2.10 m, and by 0.02 at 1.70 m, so it will not move anyone across a band on its own. It is stated rather than smoothed over.

Imperial inputs (lb, in) are converted to kilograms and meters before the calculation.

Related health calculators

Disclaimer. FFMI is a screening estimate. Body fat percentage is the largest source of error in the calculation. Not medical, fitness, or anti-doping advice. Discuss body-composition goals with a qualified professional.

Related Calculators

More tools from Health

Body Fat CalculatorEstimate body fat percentage using the U.S. Navy circumference method, with the standard fitness category scale.

Frequently asked questions

Fat-Free Mass Index is a body-composition metric similar to BMI but uses only the lean (fat-free) portion of body weight. It estimates how much muscle a person carries relative to their height. Higher FFMI usually means a more muscular build for that height.

First, fat-free mass = body weight × (1 − body fat percentage). Then FFMI = fat-free mass in kilograms divided by height in meters squared. The normalized FFMI adds a height correction (6.1 × (1.8 − height in meters)) so people of different heights can be compared on the same scale. Both versions are reported.

The bands are this page's own: below 17 below average, 17 to 20 average, 20 to 22 above average, 22 to 25 excellent for a natural lifter, and above 25 raising the possibility of enhancement. Only the last of those five numbers comes from Kouri 1995, which publishes one threshold and no scale. The other four boundaries are not in that paper and are not published by anyone this page could find. For women there is no published equivalent at all: Kouri's cohort was 157 male athletes and contained no women, so the female bands here are a shift of this page's own male bands and carry no separate evidence. Population FFMI percentiles for women do exist, but they are general-population norms rather than trained-athlete ceilings and would be the wrong thing to print here.

It comes from Kouri et al. 1995, and the paper is thinner than its reputation. Its non-user group was 74 men. Its own words: the normalized FFMI values of athletes who had not used steroids 'extended up to a well-defined limit of 25.0', and the authors concluded that 'although these findings must be regarded as preliminary, it appears that FFMI may represent a useful initial measure to screen for possible steroid abuse'. Screen for possible, and preliminary, are the authors' own hedges and they are not decoration. Kouri's own comparison group of 20 pre-steroid-era Mr. America winners averaged 25.4, above the limit. A later DXA study of collegiate American football players found 26.4 percent of them above 25 with a maximum of 31.7. Treat 25 as a screening flag, not a verdict.

FFMI is sensitive to body-fat input. A 5-point error in body fat percentage shifts FFMI by roughly 1 to 1.5 points. DEXA and BodPod are the most accurate; skinfold calipers (with a trained tester) and Navy-tape measurements are usable. Bioimpedance scales tend to read low for lean people and high for heavier people.

BMI uses total body weight, so muscle and fat count the same. Two people at the same BMI can have very different body compositions. FFMI excludes fat mass and is a better screen for muscularity, but it requires a body fat measurement and is not used by health systems for diagnosis.

No. FFMI is a rough screening number. It does not diagnose body-composition issues, fitness level, health risk, or performance-enhancing-drug use. Plenty of natural lifters score above 25 and plenty of enhanced lifters score below. Treat the number as a check, not a verdict.