How much muscle your frame can naturally carry, how far you are from that ceiling, and the body-fat range in which building muscle is most productive. Two models, based on your height, wrist, ankle and body fat.
One time only. It unlocks the tools in this browser. The tools give general, illustrative estimates for healthy adults, not medical advice.
Casey Butt’s equations, built on decades of data from drug-free competitors, predict maximum lean mass from your height, wrist and ankle: the bone measurements that set how much muscle your frame can carry. For women, the model is scaled down, so treat the result as an estimated ceiling rather than a promise.
FFMI is lean mass divided by height squared, normalised to 1.8 m. Natural ceilings sit around 25 for men and 22 for women. Where you are on this bar shows how much of your potential you have already built.
Muscle gain is most productive at about 18 to 25 percent body fat for women and 10 to 15 percent for men. Above that range, start with a fat-loss phase; below it, eat at the top of your maintenance range or in a small surplus.
The consultation is complimentary.
These tools give general estimates for healthy adults and are not medical advice. If you are pregnant, breastfeeding, under 18, or have a medical condition or a history of disordered eating, talk to your doctor before changing how you eat.
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