Free Tools
FFMI Calculator
Work out your Fat-Free Mass Index — the muscularity score that strips out body fat and adjusts for height, then shows where you sit against the documented natural muscle limit.
No sign-up, no maths. Enter your height, weight and body fat, and get your raw and height-normalised FFMI, your fat-free mass, and an honest read on the scale.
Men carry more lean mass, so the natural FFMI range sits higher than for women.
Not sure of your body fat? Estimate it first with the body fat calculator, then come back.
Enter your height, bodyweight and body fat percentage to see your FFMI.
Body composition tool
Body Fat Calculator
FFMI needs your body fat %. Estimate it here first with a tape measure, then come back.
Nutrition tool
TDEE & Macro Calculator
Building lean mass takes a small surplus and enough protein. Set the numbers here.
Body composition tool
BMI Calculator
The blunt population number FFMI improves on — see why it mislabels lifters.
Why FFMI beats BMI
BMI cannot tell muscle from fat, so it labels most serious lifters overweight. FFMI fixes that by counting only your fat-free mass — muscle, bone, organs and water — and dividing by your height squared. The result is a number that actually tracks how muscular you are for your frame, which is why coaches and researchers reach for it instead of the scale or BMI when judging physique development.
Raw vs normalised FFMI
Raw FFMI slightly favours shorter lifters, because lean mass does not scale perfectly with height squared. The normalised figure adds a small height correction back to a 1.8 metre reference, so a 165cm and a 190cm lifter can be compared fairly. When people quote FFMI numbers or the famous natural ceiling, they almost always mean the normalised value, which is the one shown as your headline result.
The natural limit — read honestly
A well-known study of drug-free bodybuilders found their FFMI clustered around 25 and rarely went higher, while steroid users reached well beyond it. That is where the idea of a natural ceiling near 25 for men comes from. Treat it as a soft statistical marker, not proof of anything: genetics, a decade of training, a low or mismeasured body fat reading, or simply being short can all lift a genuine natural above the line. The number is only as honest as the body fat percentage you feed it.
Common questions
What is FFMI?+
FFMI stands for Fat-Free Mass Index. It is your fat-free (lean) mass divided by your height squared, in the same style as BMI but counting only lean tissue rather than total weight. It is a better muscularity gauge than BMI or the scale because it strips out body fat and adjusts for how tall you are, so a lean 90kg lifter and a soft 90kg beginner get very different scores.
How is FFMI calculated?+
First your fat-free mass is your bodyweight times (1 minus your body fat percentage). That lean mass in kilograms is then divided by your height in metres squared to give raw FFMI. We also show the normalised FFMI, which adjusts the figure to a 1.8 metre reference height so taller and shorter lifters can be compared on the same scale.
What is a good FFMI?+
For men, roughly 18 to 20 is average, 20 to 22 is above average, and 22 to 25 is the well-muscled athletic range most dedicated natural lifters top out in. For women the whole scale sits lower, with about 15 to 18 covering average to athletic. Higher is more muscular for your frame, but the number depends on an honest body fat estimate.
Can FFMI tell if someone is natural?+
Not on its own. Research on drug-free bodybuilders found FFMI rarely exceeded about 25 for men, which is why a value well above that is often treated as a red flag for anabolic assistance. But it is a population correlate, not a drug test. Exceptional genetics, a very long training age, an inaccurate body fat reading, or being unusually short can all push a genuine natural above the line.
How do I raise my FFMI?+
The same way you build muscle anywhere: progressive resistance training, enough total protein (around 1.6 to 2.2 grams per kilogram of bodyweight daily), a slight calorie surplus over time, and sleep. No supplement adds meaningful lean mass on its own; the ones worth using, like whey to hit protein and creatine to support training, simply make the work more productive.
Is this medical advice?+
No. FFMI is a general, evidence-based estimate for healthy adults, not a clinical body-composition measurement or medical advice. If you have a health condition or are considering hormonal interventions, speak to a qualified clinician.
Want to move the number up?
FFMI rises when you add lean mass, and that takes training, a small surplus and enough protein. Only two supplements genuinely help the process — whey to hit your protein target and creatine to support the training — and both are scored 0–100 on the evidence.
Informational only — not medical advice. FFMI is an estimate from a field formula and depends on your body fat reading. Buy links are affiliate links; we may earn a commission at no extra cost to you.