FFMI Calculator

Find your fat-free mass by multiplying weight by one minus your body fat fraction, then divide by your height in metres squared. A 180 lb man, 5 ft 10 in, at 15 percent body fat has 153.0 lb of fat-free mass, which is an FFMI of 22.0 kg per square metre.

FFMI = fat-free mass (kg) / height (m) squared. Fat-free mass is weight x (1 - body fat / 100). The normalized FFMI adds a height adjustment of 6.1 × (1.8 - height in metres), so everyone is compared at the height of a 1.8 m person. Some calculators use 6.3 for the constant.

Fat-free mass index. It is a body composition measure like BMI, but based on the weight of everything that is not fat instead of total weight. That makes it separate from fat mass, which is why it is used to talk about muscularity. It does not measure health on its own.

There is no single good number. Schutz and colleagues found median values of 18.9 for young men and 15.4 for young women in a large Swiss sample. Higher values reflect more fat-free mass for your height, and what is right for you depends on your goals and health, so ask a professional.

The median FFMI for men aged 18 to 34 in the Schutz 2002 study of 5,635 Swiss adults was 18.9 kg per square metre, with little change with age in men. It is a reference for a general population, not for people who train, so athletes sit above it.

The median FFMI for women aged 18 to 34 in the same study was 15.4 kg per square metre, with a modest increase with age. It is a general population reference, so women who strength train will usually score higher. The calculator shows how far you are from this median.

Kouri and colleagues reported in 1995 that non-user athletes had normalized FFMI values up to about 25.0, while many steroid users exceeded it. A later critique notes the study had only 157 men and used skinfold calipers, so 25 is a sample result and not a proven biological limit.

Not proven either way. The 25 figure comes from one small 1995 study, and critics point to the sample size, the use of calipers and a reanalysis of Mr. USA competitors with a mean FFMI of 26.4. The calculator reports your number and does not judge how you got it.

The authors of the 1995 study concluded FFMI may be a useful initial screen for possible steroid abuse. It cannot show it by itself, since body fat error, height and genetics all affect the number. This calculator makes no such judgement about anyone.

It is the FFMI adjusted to the height of a 1.8 m person, because taller people naturally score higher. The adjustment is c x (1.8 - height in m). At 6 ft 3 in (1.905 m) with c = 6.1 it subtracts 0.64, and at 5 ft 4 in it adds 1.06.

Both appear. The calculator defaults to 6.1, used by Omni Calculator and quoted from the original paper by a critique. Some calculators use 6.3. The difference is small, about 0.02 for each 0.1 metre away from 1.8, and you can choose either in the calculator.

BMI uses total weight over height squared, while FFMI uses only fat-free weight. BMI equals FFMI plus the fat mass index. A 180 lb, 5 ft 10 in man at 15 percent fat has a BMI of 25.8 and an FFMI of 22.0.

Fat mass index is fat mass divided by height squared. Together with FFMI it adds up to BMI. In the example, fat mass is 12.2 kg, so FMI is 3.9. The calculator shows FMI so you can see both parts of your BMI.

It is only as accurate as the body fat figure you enter. Calipers, scales and scans differ, and a few percentage points of error moves FFMI by about a point at a typical weight. The body fat table shows the effect. Treat the result as an estimate, not a measurement.

This calculator does not estimate it. You can use a scan, a body composition scale, skinfold calipers or a professional assessment, and each has an error. Whichever you use, stick to the same method over time so changes mean something, and treat the answer as approximate.

The calculation is the same. The reference differs: Schutz found a median of 15.4 for young women against 18.9 for young men. Natural limits quoted for men come from studies of men, so the calculator makes no claim about women's limits and simply shows your number against the median.

The authors of the original study noted their formula may not be satisfactory for fat individuals. Fat mass often rises alongside lean mass, and body fat error is larger at higher fat levels. The number still calculates, but read it with caution and ask a professional.

Choose metric, enter height in cm, weight in kg and body fat percentage. A 180 cm, 85 kg person at 12 percent fat has 74.8 kg of fat-free mass, an FFMI of 23.09. Because the height is 1.8 m, the normalized value is the same.

Choose imperial, enter feet and inches for height, weight in pounds and body fat percentage. The calculator converts to kilograms and metres first: 1 lb = 0.45359 kg, 1 in = 0.0254 m. A 180 lb man at 5 ft 10 in and 15 percent fat has an FFMI of 21.95.

FFMI is fat-free mass, which includes bone, organs and water as well as muscle, so it cannot be turned into muscle alone. The lean mass table shows the fat-free mass needed at each height, for example 71.3 kg for an FFMI of 22 at 180 cm.

Different constants and rounding, different body fat inputs and different units cause small gaps. The main ones are the 6.1 versus 6.3 adjustment and whether a calculator shows the normalized or the raw value. Compare like with like, and check which one you are reading.

This calculator cannot advise on training or nutrition. FFMI rises when fat-free mass rises relative to height squared, but the right approach depends on your health and goals. Speak to a qualified coach, dietitian or doctor before changing your diet or training.

No. Lean body mass is a weight, in kilograms or pounds. FFMI divides that weight by height squared, so it can be compared between people of different heights. The calculator shows both the fat-free mass and the index. Both need a body fat figure.

No official band exists. The published numbers are the Kouri 1995 non-user limit near 25, steroid users above it, and a critique reporting a mean of 25.4 for historical bodybuilders and 26.4 in a Mr. USA reanalysis. The calculator reports your number against the median only.

No. It is an educational body composition calculation. It does not diagnose health conditions, assess steroid use, set targets or replace advice from a doctor, dietitian or coach. Use it to understand a number you already have. Ask a professional about your health.

The calculator accepts a body fat percentage above zero and below 70. Very low or very high entries are unlikely to be accurate, and body fat tools have larger errors at the extremes. Check your input method before relying on the answer.

Heights must be between 1.2 and 2.5 metres, about 3 ft 11 in to 8 ft 2 in. A value outside that range usually means the wrong unit, such as centimetres entered with imperial selected. Check the unit setting and the feet and inches boxes.

Choose imperial or metric and your sex, then enter height, weight and body fat percentage. Pick the height adjustment, 6.1 or 6.3. The results show FFMI, normalized FFMI, fat-free mass, fat mass, fat mass index, BMI and the gap to the reference median.