Body FormulaFitness

FFMI Calculator

How much lean mass you carry for your height. The one body-composition number that compares fairly between a 5 ft 6 in lifter and a 6 ft 3 in one.

Weight, height and a body-fat figure
Units
kg
cm

 

%

Measure it with a tape rather than guessing — this input drives the whole result.

Compare against

The formula is identical for everyone. Only the orientation bands differ, and they run about 3 to 4 points lower for women.

FFMI20.2

fat-free mass 65.6 kg at 1.80 m — normalised FFMI is also 20.2, because 1.80 m is the reference height

Fat-free mass 65.6 kg
Normalised FFMI 20.2
Orientation Above average

StepValueWorking
Fat-free mass 65.6 kg 80 kg × (1 − 0.18)
FFMI 20.2 65.6 ÷ 1.80²
Normalised FFMI 20.2 20.2 + 6.1 × (1.80 − 1.80)

Moving the body-fat input by three percentage points moves FFMI by about 0.8, which is a year of intermediate training progress. Compare your FFMI only against your own past figures.

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Worked example: 80 kg, 180 cm, 18% body fat

  1. Fat-free mass = 80 × (1 − 0.18) = 65.6 kg
  2. FFMI = 65.6 ÷ 1.80² = 65.6 ÷ 3.24 = 20.2
  3. Normalised FFMI = 20.2 + 6.1 × (1.80 − 1.80) = 20.2

The normalisation term is zero here because 1.80 m is the reference height the adjustment is built around. It matters for everyone else: a 1.65 m lifter with the same raw FFMI normalises to 21.1, and a 1.95 m lifter to 19.3. That correction is the whole reason the index exists in a normalised form.

Why FFMI instead of just lean mass

Lean body mass on its own is not comparable between people, because taller people carry more of everything. Dividing by height squared removes most of that, in the same way that dividing weight by height squared does — except FFMI does it to the fat-free portion only, which makes it a measure of muscularity rather than of size. It is the reason FFMI is the number bodybuilding forums argue about and other indices are not.

Reading the number

Roughly: untrained adult men cluster around 18 to 19. Several years of consistent training typically puts someone in the low 20s. The low-to-mid 20s is where lifters who have trained hard for a long time end up, and figures above about 25 are uncommon without either exceptional genetics or pharmacological help — the widely cited 25 ceiling comes from a 1995 analysis of drug-free and steroid-using bodybuilders, and it is an observation about a small sample, not a law. Women run roughly 3 to 4 points lower across the board.

These are orientation points for a training metric. They are not a grade and they carry no health meaning.

Methodology

FFMI = fat-free mass in kg ÷ height in metres squared. Fat-free mass = weight × (1 − body-fat percentage). Normalised FFMI adds 6.1 × (1.8 − height in metres), which adjusts to a 1.8 m reference so that people of different heights can be compared. Both figures are reported because both are in common use and they are frequently confused.

Limitations, stated plainly

FFMI is only as good as the body-fat percentage you feed it, and that is usually the weakest input in the chain. A 3-point error in body fat — well within the range of a tape measurement or a bio-impedance scale — moves FFMI by about 0.7, which is a year of training progress for an experienced lifter. If you are comparing your FFMI to a figure from someone else, you are comparing two estimates with error bars wider than the difference you are looking at.

The index also cannot distinguish muscle from bone, organ mass or water, and it does not know how that lean mass is distributed. Two people at FFMI 22 can look entirely different.

This is a fitness estimate, not medical advice, and not a substitute for a professional who can actually see you.

Common questions

What is a good FFMI?

For men, roughly 18 to 19 is typical without training, the low 20s reflects several years of consistent lifting, and the mid 20s is what long-term dedicated lifters reach. Women run about 3 to 4 points lower. These are orientation points from small samples, not standards — and since the calculation depends on an estimated body-fat percentage, the error on your own figure is probably larger than the gap you are comparing.

Is an FFMI over 25 possible without steroids?

The 25 figure comes from a 1995 paper comparing drug-free and steroid-using bodybuilders, in which the drug-free group clustered below it. It has since been repeated as if it were a hard ceiling, which it is not — it was an observation about a specific and small sample. Exceptionally tall, heavy-framed or genetically unusual people exceed it drug-free. It is a useful rough marker and a bad basis for accusing anyone of anything.

What is the difference between FFMI and normalised FFMI?

Raw FFMI is fat-free mass divided by height squared. Normalised FFMI adds an adjustment of 6.1 × (1.8 − your height in metres), which corrects towards a 1.8 m reference so that short and tall people can be compared on the same scale. At exactly 1.80 m the two are identical. Most published FFMI figures are the normalised version, and sites frequently report one while labelling it the other.

How much does my body-fat estimate affect FFMI?

Substantially. For an 80 kg person, moving the body-fat input from 15% to 18% changes FFMI from 21.0 to 20.2. That 0.8 difference is comparable to a year of training progress at intermediate level, and it came entirely from an input most people are guessing. Use the same body-fat method every time, and compare your FFMI only against your own past figures.

Does FFMI apply to women?

Yes, the formula is identical — there are no sex-specific coefficients. The typical values differ, running roughly 3 to 4 points lower, because women carry less lean mass for a given height on average. The normalisation term is the same.

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