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Adjusted Body Weight Calculator

Adjusted body weight (IBW + 0.4 × excess weight) for dosing and nutrition calculations.

For healthcare professionalsWeight & body compositionv1.0.1

For healthcare professionals / clinical use. Not a self-diagnosis tool.

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Enter your measurements, then press Calculate.

Methodology

Adjusted body weight with correction factor 0.4

AdjBW = IBW + 0.4 × (actual weight − IBW); IBW by Devine

Used when a drug or nutrition calculation should not use full actual weight in people with obesity. The 0.4 factor comes from aminoglycoside dosing work; the right factor depends on the drug and dosing protocol. Uses the conventional 0.4 factor; Traynor's 1995 regression gave 0.43 for overweight patients.

Who it is for
Adults whose actual weight is above ideal body weight; height 152 cm or more.
Version
1.0.1

How this calculator works

Where the formula comes from

  • Adjusted body weight adds 40% of the weight above ideal body weight to the ideal body weight: IBW + 0.4 × (actual weight − IBW). This tool uses 0.4, the commonly used convention.[1]
  • Earlier work had suggested IBW plus 40% of excess weight for aminoglycoside dosing in morbidly obese patients; a 1995 study of 1,708 patients receiving gentamicin or tobramycin found a factor of 0.43 for overweight patients.[1]

The inputs

  • The Devine ideal-body-weight equation estimates IBW as 50 kg for men or 45.5 kg for women, plus 2.3 kg for each inch of height above 5 feet.[2]

Versions and alternatives

  • Different correction factors have been proposed for different drug classes, for example about 0.3 for some beta-lactams, 0.4 for aminoglycosides and 0.45 for quinolones.[3]

Where accuracy falls (published evidence)

  • No single dosing weight suits every drug; the appropriate weight (actual, ideal or adjusted) depends on the medicine and the dosing protocol.[1][3]

What guidelines say

  • The 1995 study supports a correction factor for aminoglycoside dosing in heavier patients; it does not establish 0.4 as a universal factor for all medicines.[1]

Sources

  1. Traynor AM, Nafziger AN, Bertino JS Jr. Aminoglycoside dosing weight correction factors for patients of various body sizes. Antimicrob Agents Chemother. 1995;39(2):545–548. doi:10.1128/AAC.39.2.545
  2. McCarron MM, Devine BJ. Clinical pharmacy: case studies: case number 25 gentamicin therapy. Drug Intell Clin Pharm. 1974;8(11):650–655. doi:10.1177/106002807400801104
  3. Wurtz R, Itokazu G, Rodvold K. Antimicrobial dosing in obese patients. Clin Infect Dis. 1997;25(1):112–118. doi:10.1086/514505

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on

Worked example: how to calculate adjusted body weight

Inputs

Sex
Male
Height
170 cm
Weight
110 kg

Result

Adjusted body weight
83.6 kg (≈ 184.3 lb)
Ideal body weight (Devine)
65.9 kg (≈ 145.3 lb)
Actual weight as % of IBW
167 %

Calculation:

65.94 + 0.4 × (110 − 65.94) = 83.56

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

  • The correct dosing weight is drug-specific; check the product information or local protocol.
  • Intended for adults; children need an age- and drug-appropriate dosing method.

References

  1. Traynor AM, Nafziger AN, Bertino JS Jr. Aminoglycoside dosing weight correction factors for patients of various body sizes. Antimicrob Agents Chemother. 1995;39(2):545–548. doi:10.1128/AAC.39.2.545
  2. Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655.

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