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FFMI Calculator

Calculate your Fat-Free Mass Index (FFMI) and height-normalized FFMI from your height, weight and body fat percentage — a muscularity benchmark based on Kouri (1995).

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Height-Normalized FFMI
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All calculations happen on your device — nothing is sent externally

How to Use the FFMI Calculator

FFMI (Fat-Free Mass Index) measures how much fat-free tissue — muscle, bone and water — you carry relative to your height. It fixes a blind spot in BMI, which can't distinguish a muscular build from a fatter one, giving you a number that reflects muscularity more directly.

How to use this tool

Enter your height, weight and body fat percentage. If you don't know your body fat percentage, estimate it first with our Body Fat Calculator and come back to enter it here. The main figure shown is "Normalized FFMI", standardized to a 1.8m reference height.

Reading your results

A typical untrained adult male scores around 19-20, someone who trains regularly around 20-22, and advanced or near the natural ceiling around 22-25 (Kouri 1995). These figures are statistical tendencies and are also affected by skeletal frame and measurement error.

Building fat-free mass

Increasing fat-free mass comes down to adequate protein intake (see the Protein Calculator) combined with progressive training load (see the 1RM Calculator). Tracking FFMI periodically is a useful way to follow changes in body composition over time.

What FFMI adds over BMI

BMI only scales weight by height and cannot separate muscle from fat. FFMI scales fat-free mass by height instead, so it expresses how much lean tissue you carry for your frame. While cutting body fat, a stable FFMI is evidence that muscle has been preserved — which is why it is a better guide than judging a diet by scale weight alone.

Typical values

Untrained men usually fall around 18–20, trained lifters 20–22 and advanced lifters 22–24. The often-quoted idea that about 25 marks the natural ceiling comes from Kouri and colleagues (1995) and is a rule of thumb rather than a hard limit — frame, genetics and measurement method all produce exceptions. Women sit lower, with roughly 14–17 as the common range.

Accuracy depends entirely on the body fat figure

Because FFMI is derived from fat-free mass, any error in the body fat percentage carries straight through. Home impedance scales are accurate to about ±3–5%, which translates to roughly one point of FFMI. That makes it far more useful for tracking yourself under consistent conditions than for comparing against other people. For an estimate, see the body fat calculator.

FFMI Benchmarks (Kouri 1995, primarily for adult men)

FFMIInterpretation
Below 18Below average build
18–20Average untrained adult male
20–22Regularly trained build
22–23Advanced (near the natural ceiling)
23–25Upper range of the natural ceiling
25+Range that may exceed natural limits

Based on the study data of Kouri et al. (1995); this is not a diagnostic standard. Apply the bands to women only as a rough reference.

Glossary & FAQ

What is FFMI (Fat-Free Mass Index)?
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FFMI stands for Fat-Free Mass Index, a measure of how much fat-free mass (muscle, bone, water and other non-fat tissue) you carry relative to your height.

It is calculated as fat-free mass (kg) divided by height (m) squared — essentially a fat-free version of BMI.
Why do I need my body fat percentage to calculate FFMI?
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Fat-free mass is found by subtracting fat mass from total body weight, so your body fat percentage is needed to calculate fat mass first.

If you don't know your body fat percentage, estimate it with the Body Fat Calculator first.
Why is FFMI normalized for height?
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Taller people tend to show a lower FFMI even with comparable muscular development, so Kouri (1995) proposed a formula normalizing FFMI to a reference height of 1.8m (Normalized FFMI). This normalized value is generally used when comparing people of different heights.
What does an FFMI of 25 mean?
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In Kouri et al.'s 1995 study, nearly all subjects who had not used anabolic-androgenic steroids scored an FFMI of 25 or below.

As a result, "FFMI 25" is often cited as a rough benchmark for natural muscularity, but it is not a diagnostic threshold — it is a statistical tendency also influenced by skeletal frame and measurement error.
Does FFMI work for women?
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The formula itself applies to both sexes, but the Kouri (1995) classification bands were derived from male subjects, so applying them to women should be treated as a rough reference only. Women generally show lower FFMI values than men due to differences in body composition.
Sources
・ Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-Free Mass Index in Users and Nonusers of Anabolic-Androgenic Steroids. Clin J Sport Med. 1995;5(4):223-228.
・ Schutz Y, Kyle UUG, Pichard C. Fat-free mass index and fat mass index percentiles in Caucasians aged 18-98 y. Int J Obes Relat Metab Disord. 2002;26(7):953-960.
Disclaimer
Results reflect a statistical tendency and are not a diagnostic or medical assessment. FFMI values are affected by individual factors such as skeletal frame and measurement accuracy. Consult a doctor or professional for decisions about your health and training.

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