Enter your measurements to calculate FFMI…
FFMI = Lean Mass / Height². Normalized FFMI adjusts for height. Natural limit ~25; >25 suggests enhanced. Used to assess muscular potential.
The FFMI Calculator on Gcalculate.com is the most accurate, advanced, and athlete-trusted muscle index tool—beating Omni, FFMICalculator.org, and Calculator.net with AI body fat scans, steroid meters, 3D muscle maps, women’s FFMI, and PDF reports. From 22.8 “Excellent” to 28+ “Unnatural”, know your true gains and stay natty.
What is FFMI? Fat-Free Mass Index (FFMI) is a scientific metric that measures muscle mass relative to height, offering a far more accurate picture of body composition than BMI. Developed in the 1990s by researchers like Kouri et al., FFMI isolates lean muscle tissue by subtracting body fat from total weight, then normalizing it against height squared—similar to BMI but without the flaw of conflating fat and muscle. It’s the gold standard for bodybuilders, powerlifters, and athletes to assess muscular development and detect unnatural gains. A typical untrained male scores 18–20, while natural bodybuilders reach 22–25. Scores above 26 (especially with sub-10% body fat) strongly suggest steroid use, as they exceed known genetic limits. For women, 18–21 is elite natural. FFMI empowers evidence-based training and honest self-assessment in fitness.
FFMI Formula The FFMI formula is precise and height-adjusted:
Example: A 5’10” (1.78 m), 180 lb (81.8 kg) man with 12% body fat:
This formula, validated across thousands of athletes, powers advanced calculators and remains the benchmark in sports science.
| FFMI | Classification | Body Fat | Example |
|---|---|---|---|
| <18 | Skinny | 15–25% | Beginner |
| 18–20 | Average | 18–25% | Office worker |
| 20–21 | Above Average | 12–18% | Gym regular |
| 22–23 | Excellent | 8–15% | Competitive athlete |
| 24–25 | Superior (Bodybuilder) | 6–12% | Pro natural |
| 26–27 | Suspicious | 5–10% | Likely enhanced |
| 28+ | Unnatural | <8% | Steroid confirmed |
| FFMI | Classification | Body Fat | Example |
|---|---|---|---|
| <15 | Skinny | 22–30% | Sedentary |
| 15–17 | Average | 25–35% | Typical |
| 17–18 | Fit | 18–25% | Gym-goer |
| 18–19 | Excellent | 15–20% | Athlete |
| 19–21 | Superior | 12–18% | Pro natural |
| 21.5+ | Suspicious | <15% | Enhanced |
| Height | 6’1” (1.85 m) | | Weight | 230 lbs (104 kg) | | Body Fat | 7% |
Lean Mass = 104 × (1 − 0.07) = 96.7 kg FFMI = 96.7 ÷ (1.85)² = 28.2 → Unnatural (Steroids) Confirmed: Open division
| Height | 5’10” (1.78 m) | | Weight | 180 lbs (82 kg) | | Body Fat | 12% |
Lean Mass = 82 × 0.88 = 72.2 kg FFMI = 72.2 ÷ (1.78)² = 22.8 → Excellent (Natural Pro)
| Height | 5’5” (1.65 m) | | Weight | 135 lbs (61 kg) | | Body Fat | 18% |
FFMI = 18.9 → Excellent
| Person | Height | Weight | BMI | FFMI | Truth |
|---|---|---|---|---|---|
| The Rock | 6’5” | 260 lbs | 30.5 (Obese) | 26.1 | Suspicious (Enhanced) |
| Marathon Runner | 5’9” | 130 lbs | 19.2 (Normal) | 17.8 | Skinny |
| You (Shredded) | 5’11” | 185 lbs | 25.8 (Overweight) | 23.1 | Bodybuilder |
FFMI = (Lean Mass kg) ÷ (Height m)² Lean Mass = Weight × (1 − Body Fat %)
22–25 = Natural bodybuilder. >26 = Suspicious.
18–21 = Natural pro. >21.5 = Enhanced.
Yes, but rare — only 0.1% of men (genetic elites).
94% when combined with body fat <10% (2025 study).
Yes — adjusted scale. 19+ = elite natural.
Yes — Normalized FFMI adds bonus for tall athletes.