Tools

Find your FFMI.

Fat-Free Mass Index — a smarter, muscle-aware alternative to BMI. Enter your stats below for your raw and normalised score with a coach-floor read on where you sit.

Sex

Male Female

Units

Metric (kg / cm) Imperial (lb / ft·in)

Weight (kg)

Height (cm)

Body fat (%)

Lean mass (kg)

Enter either body-fat % or lean mass — the other updates as you type.

Read more What is FFMI? — the full story

What it measures

Fat-Free Mass Index (FFMI) quantifies lean mass (muscle, bone, organs, water — everything except fat) relative to height squared. Structurally analogous to BMI, but uses fat-free mass instead of total weight, which makes it much more meaningful for trained populations.

The formula

FFM (kg) = Weight × (1 − BodyFat%/100). FFMI = FFM ÷ Height². Normalised FFMI = FFMI + 6.3 × (1.80 − Height in m).

Why normalise?

Raw FFMI mildly disadvantages taller people — longer limbs carry more lean mass without proportionally more trunk muscle. The +6.3 correction adjusts everyone to what their score would be at exactly 1.80 m (the mean height in the 1995 reference cohort). At 1.80 m the correction is zero. The linear assumption breaks below ~5'4" and above ~6'6".

Reference ranges

Men

Normalised FFMI	Classification
< 18	Below the average gym-goer
18 – 20	Average gym-goer
20 – 22	Above average
22 – 23	Solid lifter
23 – 25	Strong natural athlete
25 – 26	At the natural ceiling
26 +	Above natural — likely enhanced

Women

Normalised FFMI	Classification
< 15	Below the average gym-goer
15 – 17	Average gym-goer
17 – 18	Above average
18 – 19	Solid lifter
19 – 21.5	Strong natural athlete
21.5 – 22	At the natural ceiling
22 +	Above natural — likely enhanced

Natural vs enhanced

The famous "FFMI 25 ceiling" for men comes from Kouri et al. (1995): 74 natural bodybuilders peaked at 25.0 (mean 21.8); 83 admitted steroid users ranged from 25.4 to 32.4 (mean 26.4). Later studies have observed natural FFMIs up to ~28 in populations selected for size, so 25 isn't an absolute lid — it's the practical ceiling for most people.

Limitations

Only as accurate as the body-fat measurement. DEXA ±1–2%, hydrostatic ±2–3%, Bod Pod ±3%, calipers ±3–4%, BIA ±4–6% (often biased low in athletes).
No frame-size correction — larger skeletons enable more lean mass.
Women's bands are extrapolated from limited data.
Water/glycogen shifts (post-workout, creatine loading, hydration) can move apparent lean mass by 2–4 kg.

Sources

Kouri EM, Pope HG Jr, Katz DL, Oliva P (1995). "Fat-Free Mass Index in Users and Nonusers of Anabolic-Androgenic Steroids." Clinical Journal of Sport Medicine 5(4):223–228.
Schutz Y, Kyle UUG, Pichard C (2002). Reference ranges in non-athletic populations.
Eckerson JM et al. (2012). "The Estimation of the Fat Free Mass Index in Athletes." Compared BIA vs DEXA.