Lean Body Weight Calculator

About this calculator

The Janmahasatian formula (2005) estimates lean body weight — total body mass minus fat mass — from total body weight, height and sex, derived by correlating dual-energy X-ray absorptiometry (DEXA) measurements against body mass index across a large population, which makes it more accurate across a wider BMI range, including obese patients, than older formulas like Hume's or Boer's. Lean body weight matters clinically because many drugs distribute mainly into lean tissue rather than fat, so dosing by total body weight in an obese patient can significantly overshoot the effective dose relative to how the drug actually distributes.

This calculator takes weight, height and sex and returns the estimated lean body weight using the Janmahasatian equation. Anesthesiologists and pharmacists calculating weight-based drug dosing, clinical researchers standardizing dosing across a study population, and dietitians estimating fat-free mass for metabolic calculations use it in place of total body weight when a drug's pharmacokinetics are better predicted by lean mass — this tool provides the estimate only and is not dosing advice.