Free tool · runs in your browser
FFMI calculator
FFMI, the fat-free mass index, is your fat-free mass in kilograms divided by your height in metres squared: BMI’s arithmetic with the fat taken out. This calculator works it out from your height, weight and body fat, estimates body fat from a tape measure if you do not know it, and sets the result beside published figures for adults and for college athletes.
Calculate your FFMI
Leave body fat empty to estimate it from the tape: neck just below the larynx, waist at the navel for men and at its narrowest for women, hips at their widest.
FFMI
21.3
With body fat estimated at 17.4% from the tape. That estimate is good to about 3.5 points either way (Hodgdon and Beckett, 1984), which puts your FFMI between 20.4 and 22.2.
Your numbers
| Body fat, tape estimate | 17.4% |
|---|---|
| Fat-free mass | 148.6 lb |
| Fat mass | 31.4 lb |
| FFMI | 21.3 |
| FFMI normalized to 1.80 m | 21.5 |
Next to published figures
| Adults at a normal BMI (Kyle et al., 2003) | 16.7 to 19.8 |
|---|---|
| Median adult aged 18 to 34 (Schutz et al., 2002) | 18.9 |
| You | 21.3 |
| Male college athletes, average (Currier et al., 2019) | 22.8 |
| Male college athletes, 97.5th percentile (Currier et al., 2019) | 28.3 |
Normalized to a height of 1.80 m, your FFMI is 21.5. That is under 25.0, where the athletes who had not used anabolic steroids topped out in the 1995 study the figure comes from (Kouri et al., 1995). FFMI cannot show how anyone built their muscle: a number under 25 proves nothing, and neither does one over it.
Show the math
- Body fat from the tape, in cm (Hodgdon and Beckett, 1984; Siri, 1961): density = 1.0324 − 0.19077 × log10(48.3) + 0.15456 × log10(177.8) = 1.0590, then 495 ÷ 1.0590 − 450 = 17.4%.
- Fat-free mass: 81.6 kg × (1 − 17.4%) = 67.4 kg.
- FFMI: 67.4 ÷ 1.778² = 21.3 kg/m².
- Normalized to 1.80 m (Kouri et al., 1995): 21.3 + 6.1 × (1.80 − 1.778) = 21.5.
For adults 19 and over. Not for pregnancy, or for anyone with a past or present eating disorder. General information, not medical advice.
What is FFMI?
FFMI is fat-free mass divided by height squared, in kg/m². Fat-free mass is everything in your body that is not fat: muscle, bone, organs and water. The index was proposed in 1990 as a way to judge lean tissue that does not depend on how tall someone is (VanItallie et al., 1990).
A 82 kg (180 lb) man at 15% body fat carries 69.4 kg of fat-free mass. At 5 ft 10 in (178 cm) that is an FFMI of 22.0. A 64 kg (140 lb) woman at 25% body fat carries 47.6 kg, and at 5 ft 4 in (163 cm) her FFMI is 18.0.
- Fat-free mass. Weight × (1 − body fat ÷ 100).
- FFMI. Fat-free mass in kg ÷ (height in m)².
- Normalized FFMI, for men. FFMI + 6.1 × (1.80 − height in m). It adjusts the result to a height of 1.80 m (Kouri et al., 1995). For the 5 ft 10 in man above it gives 22.1.
What is a good FFMI?
No body sets a scale for FFMI, so the honest answer is a comparison. The median young man is at 18.9 and the median young woman at 15.4; college athletes average 22.8 and 18.8. Many calculators print bands with labels from "average" to "suspicious" and give no source for them. Every figure below has one.
| Who | Men | Women | Source |
|---|---|---|---|
| Adults with a BMI in the normal range | 16.7 to 19.8 | 14.6 to 16.8 | Kyle et al., 2003 |
| Median adult aged 18 to 34 | 18.9 | 15.4 | Schutz et al., 2002 |
| College athletes, average (209 men, 372 women) | 22.8 | 18.8 | Currier et al., 2019; Harty et al., 2019 |
| College athletes, 97.5th percentile | 28.3 | 23.9 | Currier et al., 2019; Harty et al., 2019 |
| Highest among 74 male athletes who had not used anabolic steroids, normalized to 1.80 m | 25.0 | Not studied | Kouri et al., 1995 |
Is 25 the natural limit?
No. An FFMI of 25 is where one small sample of drug-free athletes happened to stop, not a ceiling on what the body can do. In 1995, Kouri and colleagues measured 157 male athletes: 83 who had used anabolic-androgenic steroids and 74 who had not. The normalized FFMI of those who had not reached 25.0; many of those who had went past it, and some past 30. A set of 20 Mr. America winners from 1939 to 1959, which the authors call the pre-steroid era, averaged an estimated 25.4 (Kouri et al., 1995). The authors called their findings preliminary.
Three things keep 25 from being a rule:
- Bigger samples go past it. Among 235 college football players measured by DXA, 62 (26.4%) had a height-adjusted FFMI above 25. College athletes are subject to drug testing, though the study ran no tests of its own (Trexler et al., 2017). In 209 male athletes from ten sports, the 97.5th percentile was 28.3 (Currier et al., 2019).
- The number is only as good as the body fat behind it. FFMI is BMI multiplied by the share of your weight that is not fat, so each point of body fat you are out by moves it by BMI ÷ 100: 0.26 for the 82 kg man above. The tape method’s standard error is about 3.5 points, which puts his FFMI anywhere from 21.0 to 22.9.
- It says nothing about one person. A value above 25 is uncommon, not proof of drug use, and a value under it is not proof of the opposite. FFMI describes how much fat-free mass someone carries, never how they built it.
One detail for anyone checking the arithmetic: the paper’s abstract prints the height correction as 6.3 × (1.80 − height), while later studies apply the paper’s equation with 6.1 (Trexler et al., 2017). This page uses 6.1. Between 1.50 and 2.10 m the two never differ by more than 0.06.
FFMI by weight and body fat
At one height, FFMI rises with body weight and falls with body fat. Read across from your weight to your body fat; for another height, use the calculator.
Men
| Weight | 8% fat | 10% fat | 12% fat | 15% fat | 20% fat | 25% fat |
|---|---|---|---|---|---|---|
| 60 kg (132 lb) | 17.5 | 17.1 | 16.7 | 16.1 | 15.2 | 14.2 |
| 65 kg (143 lb) | 18.9 | 18.5 | 18.1 | 17.5 | 16.4 | 15.4 |
| 70 kg (154 lb) | 20.4 | 19.9 | 19.5 | 18.8 | 17.7 | 16.6 |
| 75 kg (165 lb) | 21.8 | 21.4 | 20.9 | 20.2 | 19.0 | 17.8 |
| 80 kg (176 lb) | 23.3 | 22.8 | 22.3 | 21.5 | 20.2 | 19.0 |
| 85 kg (187 lb) | 24.7 | 24.2 | 23.7 | 22.9 | 21.5 | 20.2 |
| 90 kg (198 lb) | 26.2 | 25.6 | 25.1 | 24.2 | 22.8 | 21.4 |
| 95 kg (209 lb) | 27.6 | 27.0 | 26.4 | 25.5 | 24.0 | 22.5 |
| 100 kg (220 lb) | 29.1 | 28.5 | 27.8 | 26.9 | 25.3 | 23.7 |
| 105 kg (231 lb) | 30.6 | 29.9 | 29.2 | 28.2 | 26.6 | 24.9 |
| 110 kg (243 lb) | 32.0 | 31.3 | 30.6 | 29.6 | 27.8 | 26.1 |
Women
| Weight | 15% fat | 18% fat | 20% fat | 25% fat | 30% fat | 35% fat |
|---|---|---|---|---|---|---|
| 50 kg (110 lb) | 16.1 | 15.5 | 15.1 | 14.2 | 13.2 | 12.3 |
| 55 kg (121 lb) | 17.7 | 17.1 | 16.7 | 15.6 | 14.6 | 13.5 |
| 60 kg (132 lb) | 19.3 | 18.6 | 18.2 | 17.0 | 15.9 | 14.8 |
| 65 kg (143 lb) | 20.9 | 20.2 | 19.7 | 18.4 | 17.2 | 16.0 |
| 70 kg (154 lb) | 22.5 | 21.7 | 21.2 | 19.9 | 18.5 | 17.2 |
| 75 kg (165 lb) | 24.1 | 23.3 | 22.7 | 21.3 | 19.9 | 18.4 |
| 80 kg (176 lb) | 25.7 | 24.8 | 24.2 | 22.7 | 21.2 | 19.7 |
| 85 kg (187 lb) | 27.3 | 26.4 | 25.7 | 24.1 | 22.5 | 20.9 |
| 90 kg (198 lb) | 28.9 | 27.9 | 27.2 | 25.5 | 23.8 | 22.1 |
FFMI for women
Women’s FFMI runs lower than men’s, about 3.5 points at the median, and it has its own published figures. The median for women aged 18 to 34 is 15.4, against 18.9 for men (Schutz et al., 2002). Among 372 female college athletes measured by DXA, the average was 18.8 and the 97.5th percentile 23.9 (Harty et al., 2019).
The figure of 25 and the height correction both come from a study of men, so this calculator applies neither to women. In the athletes above, adjusting FFMI for height made no significant difference (Harty et al., 2019).
FFMI or BMI?
BMI is weight over height squared; FFMI is the same sum with the fat left out, so FFMI = BMI × (1 − body fat ÷ 100). The 82 kg man at 5 ft 10 in has a BMI of 25.8 whatever he is made of. At 15% body fat his FFMI is 22.0; at 30% it is 18.1. BMI cannot tell those two men apart, and FFMI can.
The price is the body fat figure. BMI needs a scale and a tape for your height; FFMI adds a measurement that is hard to take well, and carries its error.
Getting a body fat number
If you leave body fat empty, the calculator estimates it from your neck and waist, and your hips if you are a woman, with the equations the U.S. Navy published in 1984 (Hodgdon and Beckett, 1984a; Hodgdon and Beckett, 1984b), converting body density to body fat with Siri’s equation (Siri, 1961). Against underwater weighing those equations are good to about 3.5 points for men and 3.7 for women, which is why a tape result is shown as a range.
The body fat calculator covers the method in full: where to put the tape, the equations, and how the result compares with a DXA scan. A body fat figure also sharpens the maintenance calorie calculator and sets the protein range in the cutting calculator.
Questions
What is a good FFMI?
There is no official scale, only published figures to compare with. The median for adults aged 18 to 34 is 18.9 for men and 15.4 for women (Schutz et al., 2002). College athletes measured by DXA average 22.8 for men and 18.8 for women (Currier et al., 2019; Harty et al., 2019). A result between those two figures means more muscle for your height than most adults carry.
Is an FFMI of 25 the natural limit?
No. The figure comes from a 1995 study of 157 male athletes, in which the 74 who had not used anabolic steroids topped out at a height-normalized FFMI of 25.0 (Kouri et al., 1995). The authors called the finding preliminary. In a later study, 26.4% of 235 college football players measured by DXA were above 25 (Trexler et al., 2017).
Can FFMI tell if someone is natty?
No. FFMI describes how much fat-free mass a person carries for their height, not how they built it. A value above 25 is uncommon and proves nothing, a value under 25 proves nothing either, and the number is only as good as the body fat figure behind it: a body fat reading 3 points out moves the FFMI of a 82 kg (180 lb) man by about 0.8.
How do you calculate FFMI?
Multiply your weight by the share that is not fat to get fat-free mass in kg, then divide by your height in metres squared. A 82 kg man at 15% body fat has 69.4 kg of fat-free mass, and at 178 cm that is an FFMI of 22.0.
What is a normal FFMI for a woman?
The median for women aged 18 to 34 is 15.4, and women with a BMI in the normal range sit between 14.6 and 16.8 (Schutz et al., 2002; Kyle et al., 2003). Female college athletes average 18.8, with a 97.5th percentile of 23.9 (Harty et al., 2019). The figure of 25 comes from a study of men and does not apply.
Is FFMI better than BMI?
For describing muscle, yes. BMI counts fat and muscle alike, so a lean lifter and a heavier, fatter person can share one BMI. FFMI is BMI multiplied by the share of your weight that is not fat, which separates the two. The cost is that it needs a body fat figure and inherits that figure’s error.
Who should not use this calculator?
It is built for adults 19 and over. It is not for pregnancy, and it is not a good idea for anyone with a past or present eating disorder or for anyone whom body measurements distress. It is general information, not medical advice, and no number here is a target.
Sources
- Currier BS, Harty PS, Zabriskie HA, et al. (2019). Fat-free mass index in a diverse sample of male collegiate athletes. Journal of Strength and Conditioning Research 33(6):1474-1479. doi:10.1519/JSC.0000000000003158
- Harty PS, Zabriskie HA, Stecker RA, et al. (2019). Upper and lower thresholds of fat-free mass index in a large cohort of female collegiate athletes. Journal of Sports Sciences 37(20):2381-2388. doi:10.1080/02640414.2019.1634964
- Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy men from body circumferences and height. Naval Health Research Center, San Diego, Report No. 84-11. apps.dtic.mil/sti/tr/pdf/ADA143890.pdf
- Hodgdon JA, Beckett MB (1984). Prediction of percent body fat for U.S. Navy women from body circumferences and height. Naval Health Research Center, San Diego, Report No. 84-29. apps.dtic.mil/sti/tr/pdf/ADA146456.pdf
- Kouri EM, Pope HG Jr, Katz DL, Oliva P (1995). Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clinical Journal of Sport Medicine 5(4):223-228. doi:10.1097/00042752-199510000-00003
- Kyle UG, Schutz Y, Dupertuis YM, Pichard C (2003). Body composition interpretation: contributions of the fat-free mass index and the body fat mass index. Nutrition 19(7-8):597-604. doi:10.1016/S0899-9007(03)00061-3
- Schutz Y, Kyle UUG, Pichard C (2002). Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y. International Journal of Obesity 26(7):953-960. doi:10.1038/sj.ijo.0802037
- Siri WE (1961). Body composition from fluid spaces and density: analysis of methods. In: Techniques for Measuring Body Composition, National Academy of Sciences, pp. 223-244. Reprinted in Nutrition 9(5):480-491 (1993). pubmed.ncbi.nlm.nih.gov/8286893/
- Trexler ET, Smith-Ryan AE, Blue MNM, et al. (2017). Fat-free mass index in NCAA Division I and II collegiate American football players. Journal of Strength and Conditioning Research 31(10):2719-2727. doi:10.1519/JSC.0000000000001737
- VanItallie TB, Yang MU, Heymsfield SB, et al. (1990). Height-normalized indices of the body’s fat-free mass and fat mass: potentially useful indicators of nutritional status. American Journal of Clinical Nutrition 52(6):953-959. doi:10.1093/ajcn/52.6.953
Each figure quoted from a study was checked against the paper, or its abstract where the full text could not be read. Found an error? Email founder@topsets.app and the page will be corrected and its date updated.