Strength

FFMI Calculator

Updated 1 Nov 2026 · Source: Kouri et al. (1995) ↗

Enter your height, weight and body fat percentage. You get your lean mass, your FFMI and a height-adjusted FFMI that lets people of different heights be compared.

Worked example

Lean mass = 185 lb × (1 − 15%) = 157.3 lb = 71.3 kg
Height = 1.778 m
FFMI = 71.3 ÷ 1.778² = 22.6
Adjusted = 22.6 + 6.1 × (1.8 − 1.778) = 22.7

Lean mass (lb) for a given FFMI, by height

Height	FFMI 18	FFMI 20	FFMI 22	FFMI 25
5'4"	105	117	128	146
5'6"	112	124	136	155
5'8"	118	132	145	164
5'10"	125	139	153	174
6'0"	133	147	162	184
6'2"	140	156	171	195
6'4"	148	164	181	205

What FFMI tells you

FFMI stands for fat-free mass index. It takes your lean mass (everything that is not fat) in kilograms and divides it by your height in meters squared. Because fat is removed first, two people with the same weight can end up far apart.

With the default inputs, a 5 ft 10 in person weighing 185 lb at 15% body fat carries about 157 lb of lean mass. That works out to an FFMI of 22.6.

Why there is a height-adjusted number

To compare people of different heights, the adjusted version adds 6.1 times the difference between 1.8 m and your height, which scales everyone to a man 1.8 m (about 5 ft 11 in) tall.

If you are shorter than that, the adjusted number goes up. At 5 ft 6 in it adds about 0.8. At 6 ft 4 in it takes off about 0.8. At 5 ft 10 in the change is only 0.1, which is why the example moves from 22.6 to 22.7.

The body fat input moves everything

Your result can only be as good as the body fat number you type in. Keep the example person at 185 lb and 5 ft 10 in: at 10% body fat the FFMI is 23.9, at 20% it is 21.2. Ten points of body fat moved the result by 2.7.

Home methods can be off by several percent. Pick one method, measure under the same conditions each time, and watch the trend over months instead of trusting a single reading.

Where the 25 reference point comes from

The number most people quote traces to a 1995 study by Kouri and colleagues of 157 male athletes, 74 of whom reported never using muscle-building drugs. That group averaged an adjusted FFMI of about 22, and their values clustered up to about 25.

Treat 25 as a commonly cited reference point, not a hard limit. The same paper found champion bodybuilders from 1939 to 1959 averaged 25.4, with a high of 28.0. A later study of 235 college football players found 26.4% above 25. The 1995 study also measured body fat with calipers and had few men above 20% body fat, so it fits lean lifters best.

Using FFMI alongside your training

FFMI is most useful as a slow trend line. If it climbs while your lifts climb, your training is adding muscle. The table below the calculator shows how much lean mass each FFMI means at common heights.

Pair it with numbers that move faster, such as your lifts against the strength standards. To keep both rising, plan steady increases with progressive overload and enough weekly work from sets and reps guidance.

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Questions

Does FFMI work for women?

The formula works for anyone, but the reference numbers here come from studies of men. A woman's FFMI should not be judged against the 25 mark.

Why is my adjusted FFMI lower than my FFMI?

You are taller than 1.8 m (about 5 ft 11 in). The adjustment takes a little off for each inch above that height.

What body fat number should I enter?

Use your most recent reading from one consistent method. If you only have a guess, try a few values to see how much the result moves.

How we calculate: every formula, with its author and year, is on our method page; data sources and their licenses are on sources.

gymnical.com gives estimates from published formulas and public data. It is not medical advice and not a training prescription. Last reviewed November 2026.