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FFMI calculator

Calculate your fat-free mass index from weight, height and body fat. See where you sit on the FFMI scale, your lean mass, and how much muscle you could still add naturally.

This is not medical advice

Estimate only. Not medical advice. Check with a doctor or pharmacist before acting on it. Read the full note

These calculators use published population formulas. They do not know your medical history and cannot diagnose, treat or replace a doctor, pharmacist or dietitian. Do not change medication, dosing, eating or drinking decisions on the basis of a number here. If you are pregnant, under 18, over 65, have a health condition or take medication, ask a clinician first. In an emergency call your local emergency number.

Units
Sex
kg
cm
%

From a DEXA scan, calipers, or a visual estimate.

Where you are on the FFMI scale

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Your numbers

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How much muscle you could still add

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BMI cannot tell muscle from fat: a lean 90 kg lifter and a 90 kg sedentary person of the same height get the same score. FFMI, the fat-free mass index, fixes that by counting only lean mass. It is the standard way to compare muscularity between people of different heights, and the basis for the well-known "natural limit" of about 25.

How it is calculated

  1. Lean body mass = weight × (1 − body fat %).
  2. FFMI = lean mass (kg) ÷ height (m)².
  3. Adjusted FFMI = FFMI + 6.1 × (1.8 − height in m). This normalises everyone to 1.80 m so tall and short people can be compared on one scale.

Example

An 80 kg man, 180 cm, at 15% body fat: lean mass = 80 × 0.85 = 68 kg. FFMI = 68 ÷ 1.8² = 21.0. At exactly 1.80 m the adjustment is zero, so adjusted FFMI is also 21.0, "above average" on the male scale.

The scale and the natural limit

In a 1995 study, Kouri and colleagues measured 157 male athletes, including steroid users and lifelong drug-free lifters. No drug-free athlete exceeded an adjusted FFMI of 25, while steroid users commonly did. Later data show a few natural outliers slightly above 25, so the number is a strong signal rather than a hard law. Women carry more essential fat and less muscle, so the female scale sits about 4 points lower.

Why the body-fat estimate matters most

Weight and height are exact; body fat is a guess unless you have a DEXA scan. A 5-point error in body fat moves FFMI by about one point. If your result looks surprisingly high, the most likely explanation is that your body fat is higher than you entered.

Frequently asked questions

What is a good FFMI?

For men, 18–20 is average, 20–22 is clearly athletic, 22–25 is the range of dedicated lifters. For women, subtract about 4 from each band. Above 25 (21 for women) is rarely reached without drugs.

Is FFMI better than BMI?

For anyone who trains, yes: it separates muscle from fat. For the general population BMI is simpler and needs no body-fat estimate. The two answer different questions.

How do I find my body fat percentage?

DEXA is the most accurate consumer option. Calipers by a trained person are decent. Smart scales are the least reliable, often off by 5 points or more. Comparing yourself to reference photos gets you within a few points.

Can you have an FFMI over 25 naturally?

A small number of people do, usually with rare genetics and many years of training. If you are above 25 after a couple of years of lifting, an underestimated body fat percentage is the more likely explanation.

What is the difference between FFMI and adjusted FFMI?

Raw FFMI favours shorter people slightly. The adjusted version normalises to a height of 1.80 m so the scale applies to everyone. Use the adjusted number when comparing to the bands.

Sources

  1. Kouri EM et al. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med, 1995
  2. Schutz Y et al. Fat-free mass index and fat mass index percentiles in Caucasians aged 18–98 y. Int J Obes, 2002

By Calcelate Team. Formula from the sources above.

  1. 2026-09-14 · Formula and texts checked