Free FFMI calculator
How much lean mass do you carry for your height?
Enter your sex, height, weight and body fat %, or use a tape measure.
FFMI (fat-free mass index) is your fat-free mass in kilograms divided by your height in meters squared. A typical young man scores about 18.9 and a typical young woman about 15.4; male college athletes average about 21.5.[2][7]
FFMI at a glance
- Formula: FFMI = weight in kg × (1 − body fat % ÷ 100) ÷ height in m².
- Typical range at a normal BMI: 16.7 to 19.8 for men and 14.6 to 16.8 for women.[3]
- Low: under 17 for men and 15 for women counts as reduced muscle mass in clinical guidelines.[4]
- The “25 limit”: where drug-free male athletes topped out in a 1995 study. Later studies found college linemen above it.[1][5]
- Biggest source of error: the body fat number. Three points of body fat move FFMI by about 0.8 for a 5 ft 10 in, 180 lb man.
How to use the FFMI calculator
- Enter your sex, height and weight. The reference data are for adults.
- Add your body fat % from a DXA scan, smart scale or skinfold test. No number? Choose the tape measure and enter your neck and waist (and hips for women).
- Read your FFMI on the scale, with fat-free mass, fat mass index, and, if you set one, how much lean mass a target FFMI would take.
What is FFMI?
FFMI is BMI for lean tissue. It divides your fat-free mass (muscle, bone, organs and water) by your height squared, so people of different heights can be compared on muscle rather than total weight.[2]
BMI cannot tell muscle from fat. Two men who are both 5 ft 10 in and 200 lb have the same BMI of about 28.7, but at 12% body fat one has an FFMI of about 25.3 and at 28% the other has about 20.7. Researchers proposed FFMI and its partner, the fat mass index, to split BMI into those two parts.[3] Use the BMI calculator for the whole-weight view and the lean body mass calculator if you want lean mass in pounds or kilograms without a body fat reading.
How to calculate FFMI
Multiply your weight by (1 − body fat % ÷ 100) to get fat-free mass, then divide by your height in meters squared.
- Fat-free mass: 180 lb × 0.85 = 153 lb, or 69.4 kg.
- Height: 5 ft 10 in = 1.778 m, squared = 3.16.
- FFMI: 69.4 ÷ 3.16 = 22.0.
So a 5 ft 10 in, 180 lb man at 15% body fat has an FFMI of 22.0. A 5 ft 5 in, 140 lb woman at 25% body fat has an FFMI of 17.5. The calculator above does these steps for you, in pounds or kilograms.
Normalized FFMI
Normalized FFMI = FFMI + 6.3 × (1.80 − height in m). It adjusts men to a common height of 1.80 m, It adds a little to men shorter than 1.80 m and takes a little from taller men, so men of different heights are judged on one scale.[1]
The correction comes from the 1995 paper that also proposed the 25 limit; its abstract gives 6.3, while many websites use 6.1. The difference is under 0.1 for most heights. For the example man, normalized FFMI is 22.1. The formula was built from men only. In 372 female college athletes, height-adjusted and plain FFMI did not differ significantly, so for women this calculator shows plain FFMI.[6]
FFMI chart: what is a good FFMI?
For men, 16.7 to 19.8 is typical at a normal BMI and around 21.5 is athletic. For women, 14.6 to 16.8 is typical and around 17.9 to 18.8 is athletic.[3][7][6]
| Benchmark | Men | Women | Source |
|---|---|---|---|
| Reduced muscle mass (measured) | Under 17 | Under 15 | GLIM clinical criteria, 2019 |
| Range at a normal BMI | 16.7 to 19.8 | 14.6 to 16.8 | 5,635 Swiss adults, 2003 |
| Median, ages 18 to 34 | 18.9 | 15.4 | Same group, 2002 |
| College athletes, average | 21.5 | 17.9 | 1,961 US college athletes, 2024 |
| Top of drug-free gym athletes (1995) | 25.0 (normalized) | Not studied | 157 male athletes |
| 97.5th percentile, college athletes | 28.1 (football) | 23.9 | 235 football players, 2017; 372 women, 2019 |
“Good” depends on what you want. For health, the main concern is being under the low cut-off, especially later in life or after illness. For sport, a higher FFMI usually means more muscle to produce force. The calculator places you on a scale with these reference points rather than giving you a grade, because the reference groups differ in age, sport and measuring method.
What FFMI 20, 22 and 25 look like in numbers
At 5 ft 10 in, one FFMI point is about 7 lb of fat-free mass. FFMI 22 at 15% body fat means a weight of about 180 lb; FFMI 25 at the same body fat means about 205 lb.
| FFMI | Fat-free mass | Weight at 10% fat | Weight at 15% fat | Weight at 20% fat |
|---|---|---|---|---|
| 18 | 125 lb | 139 lb | 148 lb | 157 lb |
| 20 | 139 lb | 155 lb | 164 lb | 174 lb |
| 22 | 153 lb | 170 lb | 180 lb | 192 lb |
| 24 | 167 lb | 186 lb | 197 lb | 209 lb |
| 25 | 174 lb | 194 lb | 205 lb | 218 lb |
| 26 | 181 lb | 201 lb | 213 lb | 227 lb |
| FFMI | Fat-free mass | Weight at 20% fat | Weight at 25% fat | Weight at 30% fat |
|---|---|---|---|---|
| 15 | 90 lb | 113 lb | 120 lb | 129 lb |
| 16 | 96 lb | 120 lb | 128 lb | 137 lb |
| 17 | 102 lb | 128 lb | 136 lb | 146 lb |
| 18 | 108 lb | 135 lb | 144 lb | 155 lb |
| 20 | 120 lb | 150 lb | 160 lb | 172 lb |
| 22 | 132 lb | 165 lb | 176 lb | 189 lb |
Use your own height in the calculator: a taller person needs more fat-free mass for the same FFMI. Set a target FFMI to see the lean mass it would take and the weight that implies at your current body fat.
Is an FFMI of 25 the natural limit?
It is a guide, not a hard limit. In 1995, drug-free male athletes topped out at a normalized FFMI of 25.0, but later scan studies found about a quarter of college football players above 25.[1][5]
| Study | Who | Body fat method | Key result |
|---|---|---|---|
| Kouri 1995 | 74 drug-free and 83 steroid-using male athletes | Skinfolds | Drug-free athletes topped out at 25.0 (normalized); 20 pre-steroid-era Mr. America winners averaged 25.4; some users passed 30 |
| Trexler 2017 | 235 college football players | DXA | 26.4% above 25; average 23.7; 97.5th percentile 28.1; highest 31.7 |
| Harty 2019 | 372 female college athletes | DXA | Average 18.82; 97.5th percentile 23.9 |
| Magee 2024 | 1,961 college athletes from 10 men’s and 8 women’s sports | Air displacement | Men 21.5, women 17.9 on average |
The 1995 study compared 74 male athletes who said they had never used anabolic steroids, confirmed by urine tests, with 83 who had. The drug-free group reached a well-defined ceiling of 25.0, and 20 Mr. America winners from before steroids were available averaged 25.4. Many steroid users passed 25, and some passed 30.[1]
Later work used DXA scans on bigger, heavier athletes. Among 235 college football players, 26.4% were above 25, the 97.5th percentile was 28.1, and the highest value was 31.7, in a lineman.[5] Body fat method, body size and sport all shift the number. An FFMI above 25 is uncommon, but it cannot prove steroid use on its own.
FFMI for women
Women typically score 14.6 to 16.8, and female college athletes average about 17.9 to 18.8. In 372 female college athletes, 97.5% were under 23.9.[3][7][6]
The 25 rule was never tested in women. The largest female study found the highest averages in rugby and Olympic weightlifting and the lowest in cross country, which shows how much sport and body size matter.[6] In the Swiss population study, women’s median FFMI rose slightly with age, while men’s did not change.[2]
Low FFMI and health
A measured FFMI under 17 for men or 15 for women is one of the signs clinicians use for reduced muscle mass.[4]
The Global Leadership Initiative on Malnutrition uses reduced muscle mass, together with weight loss, low intake or illness, to diagnose malnutrition. The cut-off applies to a measured FFMI, not to a number based on a guessed body fat.[4] Muscle can be rebuilt at any age: in adults over 50, resistance training added about 1.1 kg of lean mass on average across 49 studies.[9] If your FFMI is low and you are losing weight without trying or feel weaker, talk with your doctor.
Fat mass index
Fat mass index is fat mass in kilograms divided by height in meters squared. At a normal BMI it runs from 1.8 to 5.2 for men and 3.9 to 8.2 for women.[3]
| Measure | Men | Women |
|---|---|---|
| Fat mass index, range at a normal BMI | 1.8 to 5.2 | 3.9 to 8.2 |
| Fat mass index, median | 4 | 5.5 |
| FFMI, range at a normal BMI | 16.7 to 19.8 | 14.6 to 16.8 |
FFMI and fat mass index add up to BMI. The pair shows whether a high BMI comes from muscle, fat or both. In the Swiss study, fat mass index rose by about 55% in men and 62% in women from young to old age groups, much faster than BMI.[2]
How accurate is FFMI?
FFMI is only as accurate as the body fat number behind it. The US Navy tape equations have a typical error of about 3.52 body fat points for men and 3.61 for women.[8]
| Body fat | FFMI | Normalized FFMI |
|---|---|---|
| 10% | 23.2 | 23.4 |
| 12% | 22.7 | 22.9 |
| 15% | 22.0 | 22.1 |
| 18% | 21.2 | 21.3 |
| 20% | 20.7 | 20.8 |
DXA scans are the usual research reference. Smart scales use bioelectrical impedance with their own equations, so brands differ. The tape equations were built for military screening from 594 men and 202 women and are useful when nothing else is available.[8] For tracking, use the same method, at the same time of day, every time; the calculator shows the FFMI range that the tape error implies.
How to raise your FFMI
Lift weights regularly and eat enough protein. In trials, lean-mass gains from extra protein leveled off at about 1.6 g per kilogram of body weight a day.[10]
That review pooled 49 trials with 1,863 healthy adults. Extra protein added about 0.3 kg of lean mass on average, so the training itself does most of the work.[10] Losing fat lowers your body fat but does not raise FFMI by itself. For protein-rich meals, see foods for muscle recovery and the diet guide for men, check your daily needs with the calorie calculator, and see what a recipe gives you with the nutrition calculator.
More free tools for daily health decisions.
FFMI calculator FAQ
What is FFMI?
FFMI, or fat-free mass index, is your fat-free mass in kilograms divided by your height in meters squared. It works like BMI but counts only muscle, bone, organs and water, so it shows how much lean tissue you carry for your height.
How do I calculate FFMI?
Find your fat-free mass: weight × (1 − body fat % ÷ 100). Divide it in kilograms by your height in meters squared. A 5 ft 10 in, 180 lb man with 15% body fat has 69.4 kg of fat-free mass and an FFMI of 22.0.
What is a good FFMI for men?
For men with a normal BMI, FFMI runs from about 16.7 to 19.8, and the median for young men is 18.9. Male college athletes average about 21.5. Under 17 is the cut-off clinical guidelines use for reduced muscle mass.
What is a good FFMI for women?
For women with a normal BMI, FFMI runs from about 14.6 to 16.8, and the median for young women is 15.4. Female college athletes average about 18 to 19, and 97.5% of 372 athletes in one study were under 23.9. Under 15 counts as reduced muscle mass.
What is the average FFMI?
In 5,635 Swiss adults aged 18 to 34, the median FFMI was 18.9 for men and 15.4 for women. Among 1,961 US college athletes, the average was 21.5 for men and 17.9 for women.
Is an FFMI of 25 the natural limit?
Not a hard one. In a 1995 study, drug-free male athletes topped out at 25.0. Later studies of college football players found about a quarter above 25 and a 97.5th percentile of 28.1, mostly in heavy linemen. An FFMI above 25 is uncommon but cannot prove steroid use on its own.
Is an FFMI of 22 good?
For a man, 22 is well above the 16.7 to 19.8 range seen at a normal BMI and slightly above the 21.5 average of male college athletes. For a woman, 22 is near the top of what female college athletes reach.
What is normalized FFMI?
Normalized FFMI adjusts for height so tall and short men can be compared: FFMI + 6.3 × (1.80 − height in meters), as written in the 1995 paper. Many websites use 6.1, which changes the result by less than 0.1 for most people. The correction was built for men.
Can I calculate FFMI without knowing my body fat?
Yes, roughly. This calculator can estimate body fat from your height and neck, waist and hip measurements with the US Navy tape equations. Those equations have an error of about 3.5 body fat percentage points, so treat the FFMI as a range.
What is a low FFMI?
Clinical nutrition guidelines treat a measured FFMI under 17 for men or 15 for women as reduced muscle mass, one of the signs used to diagnose malnutrition. If yours is low and you are also losing weight without trying, talk with your doctor.
Does FFMI change with age?
In a large Swiss study, median FFMI did not differ with age in men and rose slightly in women, while fat mass index rose with age. Muscle can still be built later in life: resistance training added about 1.1 kg of lean mass in adults over 50.
FFMI vs BMI: what is the difference?
BMI divides your whole weight by height squared, so muscle and fat count the same. FFMI uses only fat-free mass. Two people with a BMI of 27 can have very different FFMI values, which is why muscular people are often labeled overweight by BMI.
How much muscle do I need to raise my FFMI by 1?
One FFMI point equals your height in meters squared, in kilograms of fat-free mass. At 5 ft 10 in, that is about 3.2 kg (7 lb). Taller people need more lean mass to move the number.
Sources
- Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med. 1995;5(4):223-228. Link
- Schutz Y, Kyle UU, Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y. Int J Obes Relat Metab Disord. 2002;26(7):953-960. Link
- Kyle UG, Schutz Y, Dupertuis YM, Pichard C. Body composition interpretation: contributions of the fat-free mass index and the body fat mass index. Nutrition. 2003;19(7-8):597-604. Link
- Cederholm T, Jensen GL, Correia MITD, et al. GLIM criteria for the diagnosis of malnutrition: a consensus report from the global clinical nutrition community. J Cachexia Sarcopenia Muscle. 2019;10(1):207-217. Link
- Trexler ET, Smith-Ryan AE, Blue MNM, et al. Fat-free mass index in NCAA Division I and II collegiate American football players. J Strength Cond Res. 2017;31(10):2719-2727. Link
- Harty PS, Zabriskie HA, Stecker RA, et al. Upper and lower thresholds of fat-free mass index in a large cohort of female collegiate athletes. J Sports Sci. 2019;37(20):2381-2388. Link
- Magee MK, Fields JB, Jagim AR, Jones MT. Fat-free mass index in a large sample of National Collegiate Athletic Association men and women athletes from a variety of sports. J Strength Cond Res. 2024;38(2):311-317. Link
- Hodgdon JA, Friedl K. Development of the DoD body composition estimation equations. Naval Health Research Center Technical Document 99-2B. 1999. Link
- Peterson MD, Sen A, Gordon PM. Influence of resistance exercise on lean body mass in aging adults: a meta-analysis. Med Sci Sports Exerc. 2011;43(2):249-258. Link
- Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376-384. Link
This calculator gives estimates for adults, not a diagnosis. FFMI is only as accurate as the body fat number behind it. If your FFMI is low and you are losing weight without trying or feel weaker, talk with your doctor. Reviewed by Dr. Goutom Banik, MBBS, MPH.
