How much muscle can you build naturally? Three evidence-based estimates from your height and frame.
| Method | Lean mass | Bodyweight |
|---|
Casey Butt analyzed drug-free bodybuilders from before steroids were widespread and found that their best lean mass could be predicted from height and joint size. His formula (in inches and pounds):
max lean mass = height1.5 × (√wrist ÷ 22.667 + √ankle ÷ 17.0104) × (body fat % ÷ 224 + 1)
The body fat term reflects that people carry a little more lean mass (water, glycogen, and the tissue supporting fat) when they're less lean. Wrist and ankle size stand in for bone structure, which barely changes with training.
Fat-free mass index is lean mass divided by height squared, adjusted to a 1.8 m reference height. In 1995, Kouri and colleagues compared 157 male athletes and found that drug-free lifters rarely exceeded an FFMI of about 25, while steroid users often did. This calculator shows the bodyweight an FFMI of 25 works out to at your height and chosen body fat. For women, research is thinner; we use 21 as a rough equivalent.
Martin Berkhan, a coach known for the Leangains method, observed that drug-free men tend to top out at about their height in centimeters minus 100, in kilograms, in stage-lean condition (around 5% body fat). It's simple and surprisingly close to the other two.
Open "Compare with where you are now" and enter your current weight and body fat. The calculator works out your lean mass and shows how much of your estimated maximum you've already built. Don't know your body fat? The body fat calculator estimates it with a tape measure.
If you're early on, the gap can look big. That's normal: beginners can add lean mass quickly, and most people reach most of their potential within the first few years of consistent training. After that, progress is slower, and tracking matters more. Small, steady increases in your lifts, logged session to session in GymGod or a notebook, are how you close the last part of the gap.
To see what your ideal weight looks like at different muscle levels, try the Ideal Weight Calculator for Lifters.
For most men, the natural ceiling lands around an FFMI of 25. For a 5'10" (178 cm) man, that works out to about 193 lb (87 kg) at 10% body fat. Frame size shifts that up or down, which is what Casey Butt's formula accounts for. Progress is fastest in the first few years of consistent training; the last part comes very slowly.
Wrist and ankle circumference reflect bone structure and are hardly affected by fat or training. Casey Butt found that lifters with thicker joints carried more muscle at their best, so these two measurements help adjust the estimate to your frame.
Less so. The FFMI research and Casey Butt's data come mostly from men. Women can use these numbers as rough guides; an FFMI around 21 is often cited as a practical natural upper range for women, but the research is limited.
A small number of people do, thanks to genetics. These are estimates of what most drug-free lifters can reach, not hard limits. If you're well past them, your numbers may be off (body fat estimates are the usual culprit), or you may simply have exceptional genetics.
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