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FFMI calculator
Enter your height, weight and body fat percentage. The calculator returns your lean mass, your fat-free mass index (FFMI) and the height-normalized FFMI from Kouri et al. (1995), set against the 25.0 that the drug-free athletes in that study topped out at.
Example result
22.5
22.2
68kg
22.5 against the 25.0 that drug-free athletes topped out at in Kouri et al. (1995).
| Who | Normalized FFMI |
|---|---|
| You | 22.5 |
| Highest drug-free athlete | 25.0 |
| Mr. America winners 1939–59, average | 25.4 |
| Some steroid users | over 30 |
FFMI examples
Four lifters, four different questions. Imperial heights are in inches.
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Example 1
A reading above 25
A lifter five years in: 5 ft 9 in, 190 lb, and a smart scale that says 10% body fat.
- Height
- 69
- Weight
- 190 lb
- Body fat
- 10 %
- Normalized FFMI25.6
- FFMI25.3
- Lean mass171 lb
That lands past the 25.0 ceiling of the drug-free men in Kouri's study, but the input to doubt first is the body fat. Enter 15% for the same lifter and the score drops below 25. Get a second reading by a different method before reading anything into it.
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Example 2
A tall lifter
A 193 cm lifter at 100 kg and about 15% body fat, comparing himself with shorter training partners.
- Height
- 193
- Weight
- 100 kg
- Body fat
- 15 %
- Normalized FFMI22.0
- FFMI22.8
- Lean mass85 kg
His plain FFMI is the higher of the two numbers. Normalizing to a 1.80 m man, as Kouri did, pulls it down, which puts him on the same scale as his partners. Use the normalized figure to compare with other people and either one to track yourself.
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Example 3
Three years of lifting, measured by DXA
A woman who has lifted for three years: 165 cm, 64 kg, 22% body fat from a DXA scan.
- Height
- 165
- Weight
- 64 kg
- Body fat
- 22 %
- Normalized FFMI19.3
- FFMI18.3
- Lean mass49.9 kg
Compare her plain FFMI, not the normalized one, with female athletes: 372 female college athletes scanned by DXA averaged 18.8, and only the top 2.5% went past 23.9. She sits just under the athletes' average, with plenty of room left to grow.
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Example 4
Lean, but small
A beginner at 168 cm and 60 kg, about 12% body fat, wondering whether to bulk or cut.
- Height
- 168
- Weight
- 60 kg
- Body fat
- 12 %
- Normalized FFMI19.5
- FFMI18.7
- Lean mass52.8 kg
Low body fat and a modest FFMI means what's missing is muscle, not leanness. That points to a slow gain rather than a cut. The muscle gain calculator shows how much a first year of training can realistically add.
What is a good FFMI?
For men, the reference most calculators lean on is Kouri et al. (1995): among 157 male athletes, the normalized FFMI of those who had never used steroids reached a well-defined limit of 25.0, and 20 Mr. America winners from before the steroid era (1939 to 1959) averaged 25.4. Your result card shows both.
For the middle of the range, look at large samples of athletes. In a 2024 study of 1,961 NCAA athletes, men averaged 21.5 and women 17.9. These studies report plain FFMI, so compare them with your FFMI, not the normalized figure.
| Group | FFMI |
|---|---|
| Men, 596 NCAA athletes, average | 21.5 |
| Men, NCAA throwers, average | 25.7 |
| Women, 1,365 NCAA athletes, average | 17.9 |
| Women, 372 college athletes, average | 18.8 |
| Women, 372 college athletes, top 2.5% | above 23.9 |
FFMI for women
Kouri's sample was all men, so its 25.0 says nothing about women. The best female reference is Harty et al. (2019), who scanned 372 female college athletes by DXA: they averaged 18.8, rugby players averaged 20.1, and the 97.5th percentile was 23.9. The authors found adjusting for height made no significant difference, so those are plain FFMI values.
Women can use the calculator as is. Compare the FFMI figure with those averages, and leave the normalized one aside.
How FFMI is calculated
Lean mass is your weight minus the fat your body fat percentage says you carry. FFMI divides that lean mass in kilograms by your height in meters squared. Imperial inputs are converted at 2.54 cm per inch and 2.2046 lb per kg first.
The normalized FFMI adds 6.3 × (1.80 − height in meters), the correction Kouri et al. used to put every athlete on the scale of a 1.80 m man. Many calculators use 6.1. We use 6.3 because it is the figure in the published study the formula comes from. Between 1.65 and 1.95 m the two differ by less than 0.05.
lean mass = weight × (1 − body fat ÷ 100)
FFMI = lean mass (kg) ÷ height (m)²
normalized FFMI = FFMI + 6.3 × (1.80 − height (m))
80 × (1 − 0.15) = 68 kg lean
68 ÷ 1.75² = 22.20, shown as 22.2
22.20 + 6.3 × (1.80 − 1.75) = 22.52, shown as 22.5Make it fit you
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Measure body fat the same way each time
Stick to one method. At 190 lb, five points of body fat move FFMI by about 1.5, so switching from calipers to a smart scale can look like a change that never happened.
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Track the trend, not one reading
Re-run the calculator every two to three months with fresh numbers. A rising FFMI at steady body fat is lean mass you've added.
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Turn the gap into kilograms
At 1.75 m, every kilogram of lean mass adds about a third of a point. Divide 1 by your height in meters squared for your own figure, then see how long that takes with the muscle gain calculator.
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Pick the right number to compare
Use normalized FFMI against Kouri's 25.0 and plain FFMI against the college-athlete averages. Each reference was measured its own way.
Questions
What is a good FFMI?
For a man, about 21 to 22 matches the average college athlete and anything near 25 normalized is at the top of what drug-free athletes reached in Kouri's study. For a woman, a plain FFMI near 19 matches the average female college athlete.
Is an FFMI over 25 proof of steroid use?
No. Kouri et al. proposed it as a first screen and called their findings preliminary. A body fat reading a few points too low can push a lifter over 25 on its own, as the first example above shows.
Should FFMI be normalized with 6.1 or 6.3?
The 1995 study's abstract gives 6.3 × (1.80 − height), and that is what this calculator uses. Between 1.65 and 1.95 m the two differ by less than 0.05.
Is FFMI different for women?
Yes. Female college athletes averaged 17.9 to 18.8 in two large studies, against 21.5 for men, and the top 2.5% of 372 female athletes were above 23.9.
How accurate is FFMI?
The formula is exact; the body fat number is what moves. Use the same measurement method every time and the trend is reliable even when the absolute number is a little off.
How do I increase my FFMI?
Add lean mass: train each muscle hard enough and add load when your reps allow. The progressive overload calculator plans the jumps.
Related calculators and templates
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Muscle gain calculator
How fast you can add the lean mass FFMI measures.
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Strength calculator: how strong am I?
Your lifts against lifters of your sex and bodyweight.
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Strength standards calculator
What competitors at your bodyweight lift.
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Am I gaining muscle or fat?
How to tell without a scan.
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Newbie gains
How much of the first year's change is muscle.
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Best workout plan for muscle gain
A plan to raise the number.
Sources
- Kouri, Pope, Katz and Oliva (1995), fat-free mass index in users and nonusers of anabolic-androgenic steroids
- Harty et al. (2019), upper and lower thresholds of fat-free mass index in female collegiate athletes
- Magee, Fields, Jagim and Jones (2024), fat-free mass index in NCAA men and women athletes
Watch lean mass and strength move together
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