Body composition
What is a good FFMI? Chart, natural limit and examples
Fat-free mass index (FFMI) tells you how much lean mass you carry for your height. It has become the go-to number for lifters who want to know how muscular they really are — and the number people argue about when they ask whether a physique is “natural”. This guide explains what a good FFMI is, where the famous limit of 25 comes from, and why the result is only as good as the body-fat number you put in.
What FFMI measures
Your body weight is made of fat mass and fat-free mass. Fat-free mass — often called lean mass — includes muscle, bone, organs and water. Muscle is the part that changes most with training, so when lean mass rises while your frame stays the same, you have almost certainly built muscle.
FFMI takes that lean mass and scales it for height. A 70 kg lean mass means something different on a 165 cm lifter than on a 190 cm one, and FFMI puts both on the same scale.
FFMI vs BMI
BMI divides total body weight by height squared. It is useful for large populations but can’t tell muscle from fat, so muscular people often land in the “overweight” range. FFMI fixes that by removing fat first.
Take a 90 kg lifter who is 180 cm tall with 12% body fat. Their BMI is 27.8 — “overweight” on a standard chart. Their normalized FFMI is 24.4, which tells the real story: they are very muscular, not overweight.
How to calculate FFMI
You need three numbers: body weight, height and body-fat percentage.
Lean mass (kg) = weight × (1 − body fat %)
FFMI = lean mass ÷ height (m)²
Normalized FFMI = FFMI + 6.1 × (1.8 − height in m)
The normalized version adjusts everyone to a height of 1.80 m. Taller people naturally carry a little less lean mass per square metre of height, so without the adjustment they would look less muscular than they are, and shorter people would look more muscular. When people quote FFMI ranges, they almost always mean the normalized figure.
For example, 80 kg at 180 cm and 15% body fat gives 68 kg of lean mass. 68 ÷ 1.8² = 21.0, and because the height is exactly 1.80 m, the normalized FFMI is also 21.0. Our FFMI calculator does this for you in metric or imperial units.
What is a good FFMI?
These rule-of-thumb ranges for normalized FFMI are widely used for men:
| Normalized FFMI | Rating |
|---|---|
| Under 18 | Below average |
| 18–20 | Average |
| 20–22 | Above average |
| 22–23 | Excellent |
| 23–25 | Superior (near the drug-free limit Kouri observed) |
| Over 25 | Above the drug-free maximum Kouri observed (25) |
Most untrained men fall between about 17 and 20. After a few years of consistent training, most land between 20 and 23. Getting above 22 usually reflects years of well-planned training and nutrition, plus favourable genetics — frame size, muscle-belly length and how well you respond to training all play a part.
These bands are a guide, not clinical categories. They come from what is typical in trained populations rather than any health threshold, and there is no “bad” FFMI — only a starting point.
Where the “natural limit” of 25 comes from
The number comes from a 1995 study by Kouri and colleagues in the Clinical Journal of Sport Medicine. The researchers measured male athletes, some of whom had used anabolic steroids and some who had not, and introduced the normalized FFMI to compare them fairly across heights.
The drug-free athletes averaged a normalized FFMI of about 21.8, and none of them exceeded 25.0. Many of the steroid users did. The authors suggested that an FFMI above 25 is rarely reached without drugs.
That makes 25 a useful reference point, but not a law:
- The study measured one group of athletes, not every lifter who has ever lived.
- A small number of people — especially heavier, very lean, genetically gifted lifters — may legitimately score slightly above it.
- Body-fat measurement error can easily add a point, as the next sections show.
The second of those is worth putting a number on, because “none of them exceeded 25” is a zero count rather than a measurement, and zero counts are easy to over-read. There were 83 drug-free men in that group. The standard way to read a zero in a sample that size — the rule of three, from Hanley and Lippman-Hand — puts the upper bound at about 3.6%. In other words, as many as one drug-free man in twenty-eight could sit above 25 and a study of 83 would still have had a fair chance of finding none.
So the data supports “above 25 is rare without drugs”. It does not support “above 25 is impossible without drugs”, which is how the number usually gets used in an argument.
Worked examples
Three lifters with different builds show how weight, height and body fat interact:
| Lifter | Weight | Height | Body fat | FFMI | Normalized |
|---|---|---|---|---|---|
| Tall and lean | 70 kg | 185 cm | 10% | 18.4 | 18.1 |
| Trained, average height | 80 kg | 180 cm | 15% | 21.0 | 21.0 |
| Short, heavy and lean | 90 kg | 175 cm | 12% | 25.9 | 26.2 |
The tall, lean lifter looks athletic but carries relatively little muscle for their height. The third lifter is above 25. Before concluding anything, check their body-fat number: if they are really 16% rather than 12%, their normalized FFMI drops to about 25.0.
Why your body-fat estimate matters so much
FFMI is only as good as the body-fat percentage you feed it. Calipers, smart scales, tape formulas and even DEXA scans can differ by several percentage points for the same person on the same day. Hydration, recent meals and the skill of whoever takes the measurement all play a part.
For an 80 kg lifter at 180 cm, each 3 percentage points of body fat is 2.4 kg of lean mass — worth about 0.7 FFMI points. That is the difference between “above average” and “excellent”, created by the measuring method alone.
- Use the same method every time, at the same time of day, in the same conditions.
- Watch the trend over months rather than any single reading.
- Be sceptical of very low readings from bioimpedance smart scales — they can make FFMI look higher than it is.
- If you compare yourself with others, remember their body-fat figure may be optimistic.
FFMI for women
Research on female FFMI is much thinner, and the Kouri study only included men. On average, women carry less lean mass for their height, and typically score about 3–4 points lower than men with a similar training history.
As a rough guide, a normalized FFMI of around 17–19 already reflects substantial muscle for a woman. There is no well-established equivalent of the male natural limit, so be wary of charts that claim one.
How to raise your FFMI
FFMI only goes up when you add lean mass, so the recipe is the recipe for building muscle:
- Train with progressive overload. Aim to add weight or reps over time on compound lifts, with enough weekly sets for each muscle group.
- Eat enough protein. A 2018 meta-analysis by Morton and colleagues found the benefit of protein for muscle gain levelled off at about 1.6 g per kg of body weight a day, with some people benefiting up to about 2.2 g/kg.
- Eat enough overall. A small calorie surplus makes gaining muscle much easier, especially once you are past the beginner stage.
- Be patient. Gains are fastest in the first year or two and slow down after that. A rise of 1 normalized FFMI point in a year is a strong result for an intermediate lifter.
How to use FFMI well
FFMI is best as a personal progress marker. Measure it every few months with the same body-fat method. If your normalized FFMI rises while your body fat stays steady, you have added real muscle. Use it to judge your own training — not to police other people’s physiques.
Try the FFMI CalculatorFind your fat-free mass index and how close you are to the natural muscular limit.Frequently asked questions
What is a good FFMI for a man?
A normalized FFMI of 20–22 reflects a clearly trained physique, 22–23 is excellent and 23–25 is close to the highest levels seen in drug-free athletes. Most untrained men are between 17 and 20.
Is an FFMI over 25 proof of steroid use?
No. In Kouri et al. (1995) no drug-free athlete exceeded 25, which makes it a useful red flag, not proof. Body-fat measurement error alone can add a point or more, and a small number of genetically gifted lifters may be slightly above 25 naturally.
Should I use FFMI or normalized FFMI?
Use normalized FFMI when comparing with charts or with other people, because it adjusts for height. For tracking your own progress either works, as your height doesn’t change.
What is a good FFMI for a woman?
There is much less research on women. As a rough guide, women score about 3–4 points lower than men with similar training, so a normalized FFMI of about 17–19 already reflects substantial muscle.
How fast can I increase my FFMI?
Beginners gain muscle fastest, and gains slow down each year of training. An increase of 1 point in normalized FFMI over a year — roughly 3 kg of lean mass for someone 1.80 m tall — is a solid result for an intermediate lifter.
References
- 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. pubmed.ncbi.nlm.nih.gov/7496846/
- Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376–384. pubmed.ncbi.nlm.nih.gov/28698222/
- Hanley JA, Lippman-Hand A. If nothing goes wrong, is everything all right? Interpreting zero numerators. JAMA. 1983;249(13):1743–1745. pubmed.ncbi.nlm.nih.gov/6827763/
General fitness information, not medical advice. Figures are estimates calculated with the formulas cited above. Check with a doctor or qualified coach before major changes to diet, supplements or training. Read the full medical disclaimer and how we write and check these pages in our editorial policy.
