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FFMI Calculator: Fat-Free Mass Index
Calculate fat-free mass index (FFMI) and normalized FFMI from weight, height, and body fat percentage, with every step of the Kouri formula shown.
Estimated FFMI
20.7
kg/m²
Fat-free mass: 144.0 lb · Normalized FFMI: 20.8
Normalized FFMI adjusts FFMI to a height of 1.80 m using the Kouri et al. 1995 correction, which was developed in men.
What this means: FFMI is fat-free mass for your height. It depends on the body fat percentage you enter, so use the same body fat method each time you compare results.
FFMI = 65.32 kg ÷ (1.778 m)² = 20.7Normalized FFMI = 20.66 + 6.3 × (1.80 − 1.778) = 20.8How nearby inputs change it
This is an estimate for general fitness planning, not medical advice.
How this FFMI calculator works
This FFMI calculator finds your fat-free mass index in three steps. First, it splits your weight into fat mass and fat-free mass using the body fat percentage you enter: fat-free mass = weight × (1 − body fat % ÷ 100). Second, it converts fat-free mass to kilograms and height to meters. Third, it divides: FFMI = fat-free mass in kg ÷ (height in m)². The result is in kg/m².
Pounds convert to kilograms at 0.45359237 kg per lb, inches convert to meters at 0.0254 m per inch, and centimeters are divided by 100. Every intermediate value stays unrounded, and FFMI is rounded to one decimal only for display. Fat-free mass is shown in the unit of the weight you enter.
This page uses the simple definition of fat-free mass: weight minus estimated fat mass. It is the same split the body fat calculator shows as lean body mass when you add your weight there. Fat-free mass includes muscle, bone, water, and organs, so FFMI is not a measure of muscle alone.
FFMI formula: worked examples
Take a person who weighs 180 lb, has 20% body fat, and is 70 inches tall. Fat mass is 180 × 20 ÷ 100 = 36.0 lb, so fat-free mass is 144.0 lb, or 65.32 kg. Height is 70 × 0.0254 = 1.778 m, and 1.778² = 3.161. FFMI is 65.32 ÷ 3.161 = 20.7.
In metric units, a person who weighs 70 kg with 25% body fat and a height of 165 cm has 52.5 kg of fat-free mass. Height is 1.65 m, 1.65² = 2.7225, and FFMI is 52.5 ÷ 2.7225 = 19.3. The formula is the same in both unit systems; only the conversions differ.
Normalized FFMI: the 1.80 m height adjustment
Kouri and colleagues added a correction that normalizes FFMI to the height of a 1.8 m man: normalized FFMI = FFMI + 6.3 × (1.80 − height in m). Below 1.80 m the correction is positive, so it adds to FFMI. Above 1.80 m it is negative, so it subtracts. At exactly 1.80 m the two values are the same.
For the 70-inch example, the correction is 6.3 × (1.80 − 1.778) = 0.14, so normalized FFMI is 20.8. A person who is 75 inches tall (1.905 m) and weighs 200 lb at 15% body fat has 170.0 lb of fat-free mass and an FFMI of 21.2. The correction is 6.3 × (1.80 − 1.905) = −0.66, so normalized FFMI is 20.6. For the 165 cm metric example, normalized FFMI is 20.2.
The study behind the height adjustment used a sample of 157 male athletes, so the calculator labels the normalized value as developed in men. Raw FFMI is shown for everyone. The calculator does not add a separate adjustment for women, because the source does not provide one.
Where the body fat percentage comes from
Every FFMI starts from a body fat percentage, so the method behind that percentage matters. Tape-measure equations, skinfold calipers, bioelectrical impedance scales, and laboratory scans can give different percentages for the same person on the same day. If you do not have a figure, the Navy method body fat calculator estimates one from height and tape measurements.
Error in the body fat percentage carries straight into FFMI. At 180 lb and 70 inches tall, a body fat percentage that is 3 points too low or too high moves fat-free mass by 5.4 lb and FFMI by about 0.8. For tracking, use the same body fat method, the same scale, and a similar time of day, and compare readings over weeks rather than relying on one result.
What FFMI does and does not tell you
FFMI describes how much fat-free mass you carry for your height. It does not separate muscle from bone and water, and it does not measure strength or performance. This page reports the number and the arithmetic behind it. It does not grade the result, place it in a category, or suggest a target, and it is not a medical assessment.
The most useful comparison is with your own earlier results, measured the same way. A change in FFMI can reflect a real change in fat-free mass, a change in the body fat estimate, or both.
Source
Kouri et al., Clin J Sport Med 1995;5(4):223–228 (doi:10.1097/00042752-199510000-00003; PMID 7496846). Both equations used on this page, FFMI = fat-free mass in kg ÷ (height in m)² and the correction 6.3 × (1.80 − height in m), are stated in the published abstract of that paper.
Frequently asked questions
What is FFMI?
FFMI, or fat-free mass index, is fat-free mass in kilograms divided by height in meters squared. Fat-free mass is everything that is not fat, including muscle, bone, water, and organs. Dividing by height squared puts people of different heights on the same scale.
How do I calculate FFMI?
Find fat-free mass first: weight × (1 − body fat % ÷ 100). Convert it to kilograms and your height to meters, then divide fat-free mass by height squared. At 180 lb, 20% body fat, and 70 inches tall, fat-free mass is 144.0 lb (65.32 kg), height is 1.778 m, and FFMI is 20.7.
What is normalized FFMI?
Normalized FFMI adds 6.3 × (1.80 − height in meters) to FFMI, which adjusts the value to a reference height of 1.80 m. The correction comes from Kouri et al., Clin J Sport Med 1995;5(4):223–228, a study of men. For the 180 lb, 20%, 70-inch example, normalized FFMI is 20.8. At exactly 1.80 m, normalized FFMI equals FFMI.
Do I need my body fat percentage to calculate FFMI?
Yes. FFMI starts from fat-free mass, which comes from body fat percentage. If you do not have a figure, the body fat calculator estimates one from tape measurements. Any error in the percentage carries into FFMI: at 180 lb and 70 inches, 3 points of body fat moves FFMI by about 0.8.
Can women use this FFMI calculator?
Yes. The FFMI formula is the same for everyone and does not use sex, so the calculator has no sex field. The 1.80 m height adjustment was developed in a study of men, so the normalized value is labeled that way. EVR does not apply a separate adjustment for women because the source does not provide one.
Is FFMI the same as fat-free mass?
No. Fat-free mass is a weight in pounds or kilograms. FFMI divides fat-free mass in kilograms by height in meters squared, so its unit is kg/m². The calculator shows both.
Does this calculator rate my FFMI?
No. It reports the number and shows the arithmetic. It does not grade the result, compare it with groups, or set a target. Compare your own readings taken the same way over time.