FFMI calculator: how much muscle do you carry for your height?
This FFMI calculator works out your fat-free mass index: your lean body mass — everything that is not fat — divided by your height squared. It is like BMI, but because it removes body fat it describes muscularity rather than size. Enter your height, weight and body fat percentage, in centimetres and kilograms or feet, inches and pounds, and you get the plain FFMI, the height-normalised FFMI, lean and fat mass, and the fat mass index.
Lifters use FFMI as a fairer yardstick than the scale, and many want to know where they stand against the famous “natural limit of 25”. The calculator works for men and women and runs entirely in your browser.
How to use the FFMI Calculator
- Choose Male or Female and your units (cm · kg or ft · lb).
- Enter your height and weight.
- Enter your body fat %. It is required: without it there is no fat-free mass to index. If you do not know it, estimate it with the body fat calculator first.
- Read your normalised FFMI, the marker on the scale and the shaded band showing how much a ±3-point body fat error would move it.
- Optionally type a Goal FFMI to see how much lean mass — and roughly what body weight — that target needs at your height.
FFMI Calculator features
Both formulas
Plain FFMI = lean mass ÷ height² and the normalised value with the Kouri height correction, shown together with the full working.
Male and female references
Your result is compared with the median FFMI of young adults — 18.9 for men and 15.4 for women — from a study of 5,635 Swiss adults.
Error band
Body fat estimates are rarely better than ±3 points, so the scale shades the FFMI range that uncertainty produces.
Goal planner
Turns a target FFMI into the lean mass you would need and the matching body weight at your current body fat.
Metric and imperial
Switch units at any time; your height and weight are converted, not lost.
The FFMI formula and the height correction
Fat-free mass (kg) = weight × (1 − body fat % ÷ 100). Then FFMI = fat-free mass ÷ height (m)², in kg/m². Example: 80 kg at 15% body fat is 68 kg lean; at 1.78 m, FFMI = 68 ÷ 1.78² = 68 ÷ 3.1684 = 21.46.
Taller people carry slightly more lean mass per square metre, so Kouri, Pope, Katz and Oliva (Clinical Journal of Sport Medicine, 1995) added a small correction to scale everyone to a 1.80 m man: normalised FFMI = FFMI + 6.1 × (1.80 − height in m). For the example, 21.46 + 6.1 × 0.02 = 21.58. The paper’s abstract gives the coefficient as 6.3; most calculators, and this one by default, use 6.1. The choice changes the answer by at most a few hundredths, and you can switch it in the Height correction menu.
What the numbers mean
Two published reference points are used. In Schutz, Kyle and Pichard’s 2002 study of 5,635 healthy Swiss adults (International Journal of Obesity), the median FFMI at 18–34 years was 18.9 kg/m² for men and 15.4 kg/m² for women. In Kouri’s 1995 study of 157 male athletes, the normalised FFMI of the 74 who did not use anabolic steroids reached a well-defined limit of 25.0, while many users exceeded it. The medians are unadjusted values, so the calculator compares them with your unadjusted FFMI; the 25.0 limit is a normalised value. Because the height correction was built for men, women should compare the unadjusted figure.
That 25 has become the internet’s “natural limit”. Treat it with care: the authors called the findings preliminary, the sample was small and male-only, and a few well-documented drug-free athletes exceed it. A high reading is far more often a body fat measurement that is too low — a smart scale saying 8% when a DEXA scan would say 13% adds more than one FFMI point for a typical lifter.
| Example | Height | Weight | Body fat | FFMI | Normalised |
|---|---|---|---|---|---|
| Man | 1.75 m | 72 kg | 18% | 19.3 | 19.6 |
| Trained lifter | 1.80 m | 85 kg | 13% | 22.8 | 22.8 |
| Woman | 1.65 m | 60 kg | 28% | 15.9 | 16.8 |
| Trained woman | 1.68 m | 62 kg | 20% | 17.6 | 18.3 |
Getting a reliable result
- Use the best body fat figure you have. DEXA or hydrostatic weighing beats calipers, which beat tape formulas and bathroom scales. Use the same method each time you compare.
- Weigh in the morning after the toilet and before eating or drinking; daily water swings move lean mass by a kilogram or more.
- Track the trend, not one number. A change of 0.5 FFMI over a year of training is real progress for an experienced lifter.
- FFMI ignores where the muscle is and how strong it is. Pair it with the one rep max calculator for strength, and the protein calculator when building lean mass.
FFMI Calculator FAQ
How do I calculate FFMI?
Multiply your weight by (1 − body fat percentage) to get fat-free mass in kilograms, then divide by your height in metres squared. For the normalised FFMI, add 6.1 × (1.80 − your height in metres). The FFMI calculator above does both and shows the working.
What is a good FFMI for a man?
The median for young adult men is about 18.9. Values in the low 20s are typical of people who train regularly, and the 1995 Kouri study found that drug-free male athletes topped out at a normalised FFMI of about 25. “Good” depends on your goals; FFMI is not a health score.
What is a normal FFMI for a woman?
In the large Swiss reference study the median FFMI for women aged 18–34 was 15.4. Trained women commonly reach 17–19. The 25 benchmark comes from men and does not apply to women.
Is an FFMI over 25 proof of steroid use?
No. The authors proposed FFMI only as an initial screening idea from a small sample. Measurement error in body fat is the most common reason for a very high result, and some drug-free athletes exceed 25.
Why does the calculator need my body fat percentage?
FFMI is built on fat-free mass, which you can only get by removing fat mass from total weight. Without a body fat figure the result would just be BMI. If you have no measurement, the body fat calculator gives a tape-measure estimate.
What is the difference between FFMI and BMI?
BMI divides total weight by height squared, so it cannot tell muscle from fat. FFMI uses only lean mass. Compare with the BMI calculator.