MasterTool

FFMI Calculator

Calculate your fat-free mass index (FFMI) and height-normalised FFMI from weight, height and body fat percentage.

Loading calculator…

What this tool does

Calculate your fat-free mass index (FFMI) and height-normalised FFMI from weight, height and body fat percentage. Accuracy depends entirely on the body-fat input — use a consistent method (e.g. the Navy tape estimate on this site). Published FFMI reference ranges come from Kouri et al. (1995).

How to use the FFMI Calculator

  1. Enter or select body weight in lb.
  2. Enter or select height in in.
  3. Enter or select body fat (%).
  4. Read the calculated result; change any measurement to compare alternatives.

Formula

fat-free mass = weight × (1 − body fat %); FFMI = FFM kg / height(m)²; normalised FFMI = FFMI + 6.1 × (1.8 − height m)
weight
Body weight (lb, before metric conversion)
height
Height (in, before metric conversion)
bf
Body fat (%)

Accuracy depends entirely on the body-fat input — use a consistent method (e.g. the Navy tape estimate on this site). Published FFMI reference ranges come from Kouri et al. (1995).

Worked example

For ffmi calculator, the following measurements illustrate the exact method: Body weight: 180; Height: 70; Body fat (%): 15.

Inputs

  • Body weight180 lb
  • Height70 in
  • Body fat (%)15

Result

  • Fat-free mass153 lb
  • FFMI21.95
  • Normalised FFMI (to 1.8 m)22.09

Results explained

Fat-free mass
Fat-free mass from the formula above, expressed in lb before metric conversion. Accuracy depends entirely on the body-fat input — use a consistent method (e.g. the Navy tape estimate on this site). Published FFMI reference ranges come from Kouri et al. (1995).
FFMI
FFMI from the formula above. Accuracy depends entirely on the body-fat input — use a consistent method (e.g. the Navy tape estimate on this site). Published FFMI reference ranges come from Kouri et al. (1995).
Normalised FFMI (to 1.8 m)
Normalised FFMI (to 1.8 m) from the formula above. Accuracy depends entirely on the body-fat input — use a consistent method (e.g. the Navy tape estimate on this site). Published FFMI reference ranges come from Kouri et al. (1995).

Frequently asked questions

Fat-free mass index scales your lean (non-fat) mass by height squared, like a BMI for muscle and other lean tissue: FFMI = fat-free mass in kg ÷ height in metres squared.

In the classic Kouri et al. study, non-steroid-using men averaged around 21–22, with about 25 proposed as an upper natural limit; women's values run lower. These are research reference points, not pass/fail lines.

Raw FFMI slightly favours taller lifters. The normalised version adjusts everyone to a 1.8 m reference height (adding 6.1 × (1.8 − height in m)) so lifters of different heights compare fairly.

Only as accurate as your body-fat estimate. A 3-point body-fat error moves FFMI by roughly a full point, so use the same measurement method every time and track the trend.

No. FFMI is a population statistic with natural variation in genetics, frame and measurement error. It cannot prove or disprove anything about an individual.