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About this tool
Fat-free mass index and height-normalised FFMI from weight, height and body fat percentage, with natural-limit context for lifters.
Fat-Free Mass Index (FFMI) is lean body mass in kilograms divided by height in metres squared — the muscularity measure BMI cannot give, because BMI cannot tell muscle from fat. This calculator also reports the height-normalised FFMI from Kouri et al. (1995), which adds 6.1 x (1.8 - your height in metres) so lifters of different heights land on one comparable scale. It is aimed at people tracking a bulk or cut who already have a body fat measurement.
Open FFMI Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Applies the Kouri 6.1 coefficient so a 1.65 m and a 1.90 m lifter can be judged on the same number.
Reports the lean mass and scale weight that would put you exactly at the drug-free ceiling for your height.
Takes kilograms and centimetres or pounds and feet-inches, using exact conversion factors.
For men, a normalised FFMI of 18 to 20 is average for the untrained, 20 to 22 reflects a year or two of training, 22 to 24 is well-muscled and 24 to 25 sits at the drug-free ceiling. For women the equivalent bands run roughly 14 to 16 average, 16 to 18 above average, 18 to 20 excellent and 20 to 22 near the ceiling.
FFMI = fat-free mass (kg) divided by height (m) squared, where fat-free mass is total weight multiplied by (1 minus body fat percentage / 100). The normalised version adds 6.1 x (1.8 - height in metres) to correct the residual bias toward taller people, so an 80 kg man at 180 cm and 15 percent body fat has 68 kg lean mass and an FFMI of 21.0.
No. Kouri and colleagues found that essentially no drug-free athlete in their sample exceeded a normalised FFMI of about 25, which is why 25 is quoted as a practical ceiling — but it is a population observation, not a test. An underestimated body fat percentage is by far the most common reason for an implausibly high result, since a 5-point error moves FFMI by more than a full point.
For anyone who trains, yes — BMI counts muscle and fat identically, so a lean 85 kg lifter at 180 cm is classed overweight at a BMI of 26 while his FFMI shows the mass is lean. FFMI's weakness is that it needs a body fat measurement, so it inherits all the error of calipers, bioimpedance scales or DEXA.
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