By Zencalcy Editorial TeamLast reviewed About us
Adjusted body weight (ABW) is a dosing estimate used when a person weighs substantially more than their ideal body weight. It adds 40% of the excess weight to the ideal figure, approximating how some drugs distribute into lean and fat tissue. It is a clinical convention, not a measurement of true lean mass.
Estimate dosing weight when actual weight exceeds ideal weight.
IBW (men) = 50 + 2.3 × inches over 5 ft IBW (women) = 45.5 + 2.3 × inches over 5 ft ABW = IBW + 0.4 × (actual weight − IBW)
When actual weight is at or below IBW, the adjusted value equals actual weight because no excess correction applies. The 0.4 factor is a pharmacokinetic rule of thumb; specific drugs have their own dosing weight guidance and some use lean body weight or total body weight instead.
| Symbol | Meaning |
|---|---|
| IBW | Ideal body weight from the Devine formula, in kg. |
| ABW | Adjusted body weight used for some dosing calculations, in kg. |
| 0.4 | Convention that 40% of excess weight behaves like lean tissue for drug distribution. |
180 cm is 70.87 inches, or 10.87 inches over 5 feet. IBW = 50 + 2.3 × 10.87 = 75.0 kg. Excess weight is 110 − 75.0 = 35.0 kg, so ABW = 75.0 + 0.4 × 35.0 = 89.0 kg.
Many drugs distribute mainly into water and lean tissue rather than fat. In a person with obesity, scaling a dose directly to total body weight can overshoot exposure, while using ideal body weight can undershoot it. Adjusted body weight sits between the two and is widely taught as a practical compromise. The 0.4 factor is not derived from a single physiological constant; it is an empirical convention that has survived because it performs reasonably in studies of several drugs. Modern practice increasingly uses lean body weight equations or population pharmacokinetic models for specific agents. The practical message is that ABW is a starting point for a dosing discussion, not an automatic prescription. Renal function, age, interacting medicines and the drug's own distribution profile all change the final dose.
Continue with the ABSI Calculator (A Body Shape Index), BAI Calculator (Body Adiposity Index), or the Body Frame Size Calculator — or browse more body measurements tools and all health calculators.
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It is used in some drug dosing protocols for people with obesity, particularly for medications that distribute partly into adipose tissue. It is not a universal dosing weight and should never replace drug-specific guidance.
Every result is a screening estimate from published anthropometric equations, not a diagnosis or a measurement of body composition. Tape measurements should be taken snugly against the skin without compressing it, at the landmarks named in each tool. Equations were derived in specific populations and can be less accurate for athletes, older adults, children, pregnant people and people with significant oedema.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026