CALCULATOR

FFMI Calculator

Fat-free mass index: lean mass relative to height, with the normalised figure and an honest note on the so-called natural limit.

Fat-free mass index

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FFMI–

Normalised FFMI–

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Fat-free mass–

Fat mass–

Weight at FFMI 22, same body fat–

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What FFMI measures

Fat-free mass index describes how much lean mass you carry relative to your height. It is calculated the same way BMI is, but using fat-free mass instead of total weight, which removes BMI biggest flaw: its inability to distinguish muscle from fat.

The normalised version adjusts for height, because taller people naturally score slightly lower on the raw index. Most published categories use the normalised figure.

FFMI is genuinely useful for tracking your own lean mass over months, since it holds height constant and strips out fat changes. It is less useful as a comparison against other people, and the widely quoted natural limit deserves scepticism.

Frequently asked questions

What is a good FFMI?

For men, around 20 is average, 22 is above average and 23 or higher indicates substantial training. For women the equivalent figures sit roughly 4 points lower.

Is FFMI 25 the natural limit?

That figure comes from a single 1995 study of a small sample and has been heavily over-interpreted. It is a rough observation, not a biological ceiling.

How is FFMI different from BMI?

BMI uses total weight; FFMI uses fat-free mass. FFMI therefore separates muscle from fat, which BMI cannot.

Do I need body fat percentage?

Yes. Without it the calculation cannot be done, and the accuracy of your result depends on that measurement.

Sources

Kouri EM, Pope HG, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clinical Journal of Sport Medicine, 1995.
Schutz Y, Kyle UUG, Pichard C. Fat-free mass index and fat mass index percentiles. International Journal of Obesity, 2002.
National Institutes of Health, Office of Dietary Supplements. Nutrient fact sheets. ods.od.nih.gov
NHS. Nutrition and health guidance. nhs.uk
US Departments of Agriculture and Health and Human Services. Dietary Guidelines for Americans, 2025-2030. dietaryguidelines.gov

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General information, not medical advice. Consult a qualified professional before changing your diet, especially with a medical condition.