Nishaana
FFMI calculator — your fat-free mass index.
Your fat-free mass index (FFMI) is your lean mass scaled to your height — a muscularity score that BMI can't give. This calculator takes your height, weight, and body-fat % to find FFMI and Kouri's height-normalized FFMI, then shows where you sit against the ~25 natural limit. Metric or imperial, live, no signup.
FFMI ranges.
Normalized FFMI bands. These match the sex you selected — women run about 4 points lower at each tier.
| Level | Normalized FFMI | Who it fits |
|---|---|---|
| Below average | under 18 | Little muscle developed |
| Average | 18 – 20 | Untrained to lightly trained |
| Above average | 20 – 22 | A few solid years of training |
| Excellent | 22 – 23 | Advanced natural lifter |
| Superior | 23 – 25 | Near the natural genetic ceiling |
| Suspicious of natural | 25+ | Rare naturally — Kouri's data topped out at 25 |
| Level | Normalized FFMI | Who it fits |
|---|---|---|
| Below average | under 14 | Little muscle developed |
| Average | 14 – 16 | Untrained to lightly trained |
| Above average | 16 – 18 | A few solid years of training |
| Excellent | 18 – 20 | Advanced natural lifter |
| Superior | 20 – 21 | Near the natural genetic ceiling |
| Suspicious of natural | 21+ | Rare naturally for women |
The ~25 ceiling comes from Kouri's 1995 study: across 74 drug-free athletes, the highest normalized FFMI was exactly 25.0, and a sample of pre-steroid-era Mr. America winners averaged 25.4. It's a strong benchmark, not a physical wall — and FFMI is only as honest as the body-fat % you feed it. A wildly wrong body-fat guess produces a wildly wrong FFMI.
The FFMI formula, explained.
Three steps: strip out fat, scale to height, then normalize for stature. Heights in metres.
LBM = weight × (1 − BF% ÷ 100) Fat-free mass — muscle, bone, water, organs — after removing the fat portion of your bodyweight.
FFMI = LBM(kg) ÷ height(m)² Lean mass scaled to height, the same way BMI scales total weight — but built only from fat-free tissue.
FFMIₙ = FFMI + 6.1 × (1.8 − height_m) Kouri's height correction to a 1.8 m reference — the figure used for the ~25 natural limit.
Worked example: an 80 kg, 178 cm man at 15% body fat has 68 kg of lean mass. FFMI = 68 ÷ 1.78² = 21.5. Normalized = 21.5 + 6.1 × (1.8 − 1.78) = 21.6 — above average, with real natural room to grow. Source: Kouri EM et al., Clin J Sport Med, 1995.
Related body calculators.
Get the lean mass and body fat FFMI needs — then track your muscularity in the browser.
Lean body mass calculator
The Boer, James, and Hume formulas that feed FFMI.
Open toolBody-fat calculator
The US Navy method to get the body-fat % this tool needs.
Open toolBMI calculator
The muscle-blind screen FFMI was built to replace for lifters.
Open toolNutrition tracker
Log food against your numbers, right in the browser.
Open toolFat-free mass index questions.
What is a good FFMI?
For men, an FFMI of 18 to 20 is average, 20 to 22 is above average after a few years of training, and 22 to 25 marks an advanced-to-superior natural lifter. Women run roughly 4 points lower at each tier. In Kouri's 1995 study of drug-free athletes the highest natural FFMI recorded was 25.0, so a normalized FFMI in the 22 to 24 range is an excellent, realistic natural target.
What is the difference between FFMI and normalized FFMI?
Raw FFMI is your fat-free mass in kilograms divided by your height in metres squared. Because taller people tend to carry more absolute muscle, Kouri added a height correction — + 6.1 × (1.8 − height in metres) — to compare everyone to a 1.8 m reference. That adjusted figure is normalized FFMI, and it is the number used when people cite the ~25 natural limit.
Is an FFMI of 25 really the natural limit?
It is a strong data-backed benchmark, not a hard wall. Kouri's 1995 study of 74 drug-free athletes found none exceeded a normalized FFMI of 25.0, and a sample of pre-steroid-era Mr. America winners averaged 25.4. A handful of exceptional or very lean individuals can nudge slightly past it, but a sustained normalized FFMI well above 25 is uncommon without pharmacological help.
How do I lower my body fat to improve FFMI?
You don't lower body fat to raise FFMI directly — FFMI is built from fat-free mass, so it rises when you gain muscle, not when you diet. What body fat does is make the number honest: an accurate body-fat percentage means the fat-free mass FFMI uses is real muscle, bone, and water rather than an inflated figure. Measure body fat carefully, then chase FFMI through training.
Does FFMI work for women?
Yes, with different reference ranges. The formula is identical, but because women carry less muscle relative to height, their FFMI values run about 4 points lower at every tier — average around 14 to 16, excellent around 18 to 20. This calculator applies the correct band table for the sex you select.
Is this FFMI calculator free?
Yes. It computes in your browser, updates as you type, and needs no signup. Save your result to Nishaana to track your FFMI and lean mass as you train.
Save your numbers. Track them.
Free in your browser — Nishaana keeps your FFMI, lean mass, and body fat together and charts them as you train, no app store needed.
Start free