Body composition calculator
Adjusted body weight calculator
Devine ideal body weight, and the adjusted body weight derived from it. Enter height and weight. Free, instant, no sign-up.
Actual weight is more than 120 % of ideal, which is the conventional point at which adjusted body weight is used instead of actual or ideal.
Ideal body weight is a dosing convention, not a goal weight. The coach works from what you actually want.
What is adjusted body weight?
Adjusted body weight is a compromise number used when neither actual nor ideal body weight is the right scalar for a calculation. It is defined as ideal body weight plus 40 % of the difference between actual and ideal weight. It exists almost entirely for clinical purposes — weight-based drug dosing, nutritional requirement estimates, ventilator settings — and it is a convention rather than a measurement of anything.
Where the 40 % comes from
A drug that distributes into body water does not distribute evenly into every kilogram of a heavier body, because adipose tissue is roughly 30 % water against lean tissue's 70 %. Dose on actual weight and you overshoot; dose on ideal weight and you undershoot, because the extra tissue is not inert — it comes with additional blood volume and lean mass. The 0.4 factor is the empirical middle: about 40 % of excess mass behaves, for distribution purposes, like the compartment the drug goes into. Ideal body weight itself comes from Devine's 1974 equation: 50 kg for men and 45.5 kg for women at five feet, plus 2.3 kg for every inch above that.
What this number is not
It is not a goal weight, and Devine's ideal body weight is not a health target either. Devine proposed it as a rule of thumb for gentamicin dosing; it was never validated as a description of what anyone should weigh, and it takes no account of frame size, muscle mass or body composition. A lean, muscular athlete routinely exceeds 120 % of Devine ideal weight with nothing wrong. Which weight descriptor any particular drug or calculation uses is specific to that drug and belongs to whoever is prescribing — this page is a reference calculation, not a dosing recommendation.