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FFMI calculator
Your fat-free mass index from height, weight and body fat — a description of your current build, not a ceiling.
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Short answer: FFMI is your fat-free mass in kg divided by your height in metres squared. It describes how much lean mass you carry for your height.
- Fat-free mass
- 65.6 kg
- FFMI
- 20.7
- Height-normalised FFMI
- 20.8
20.7
Fat-free mass 65.6 kg · normalised 20.8
Fat-free mass is your bodyweight minus the fat implied by your body-fat percentage — everything that is not fat. FFMI is fat-free mass (kg) divided by height (m) squared; the normalised figure adjusts it to a height of 1.8 m (Kouri et al., 1995). The result is only as accurate as your body-fat estimate, which can easily be several percentage points out. It describes your current build; it is not a limit on what you can achieve. Your body figures stay on this device so the Hub's other calculators can fill them in for you, and are never sent anywhere.
How the FFMI formula and normalised FFMI work
Fat-free mass is your bodyweight minus your fat mass. FFMI divides that by your height in metres squared. Normalised FFMI then adjusts the score to a height of 1.8 m (Kouri et al., 1995), so people of different heights can be compared.
What your FFMI score means for men and women
Women usually carry less lean mass than men at the same height, so their scores tend to be lower. Use your score to track change over time rather than to judge yourself against others.
FFMI and natural muscle-building limits
FFMI describes your current build; it is not a hard limit. For a model of how much more muscle you might add, try the genetic muscular potential calculator.
Frequently asked questions
How accurate is FFMI?
Is FFMI better than BMI?
How do I measure my body fat?
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How the calculation works
Fat-free mass = bodyweight × (1 − body-fat percentage ÷ 100). FFMI = fat-free mass in kg ÷ height in metres squared. Height-normalised FFMI adds 6.1 × (1.8 − height in metres), following Kouri et al. (1995). Results are rounded to one decimal place after calculation.
Worked example
At 80 kg, 180 cm and 15% body fat, estimated fat-free mass is 68 kg. Dividing by 1.8 squared gives FFMI 21; height-normalised FFMI is also 21, because the example height is 1.8 m.
What the result cannot tell you
Fat-free mass includes everything that is not fat, not just skeletal muscle. An inaccurate body-fat estimate changes both results. FFMI cannot establish a person's natural potential, prove drug use or predict how much muscle they can gain.
Common questions
Does FFMI measure muscle alone?
No. It uses estimated fat-free mass, which also includes water, bone and other non-fat tissue.
Is there a universal natural FFMI limit?
This calculator does not apply a natural limit or classify anyone's drug use. It describes the entered measurements.
Why show two FFMI figures?
The first uses your actual height. The second applies the published adjustment to a reference height of 1.8 metres.
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Educational information for adults aged 18 and over. It does not diagnose, treat or manage any medical condition. If you have a health condition, or symptoms that worry you, speak to your doctor or a health professional.