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Adjusted Body Weight Calculator
Computes ideal body weight (Devine) and adjusted body weight (IBW + 0.4 × (actual − IBW)) used for drug dosing and creatinine clearance in people whose weight exceeds 120% of ideal.
When to use
You need the dosing weight for hydrophilic drugs (e.g. aminoglycosides) or the Cockcroft-Gault weight in an overweight adult.
Do not use when: The drug is dosed on actual weight (many lipophilic drugs), the person is under 18 or shorter than 152 cm, where Devine's formula is not validated.
Formula
IBW = 50 (male) or 45.5 (female) + 2.3 × (height_cm / 2.54 − 60); adjusted_BW = IBW + correction_factor × (weight_kg − IBW), applied when weight_kg > 1.2 × IBW
The 0.4 factor assumes about 40% of excess adipose tissue is water and drug-distributing; it is a convention from aminoglycoside pharmacokinetics rather than a universal rule, and drug-specific labelling takes precedence. Results are informational only and not a substitute for clinical judgement or medical advice.
Inputs
| Parameter | Type | Unit | Required | Description |
|---|---|---|---|---|
sex | enum: male | female | yes | Sex used to select the formula coefficients or thresholds. | |
height_cm | number | cm | yes | Height in centimetres. Range: ≥ 120, ≤ 260 |
weight_kg | number | kg | yes | Actual body weight in kilograms. Range: > 0, ≤ 700 |
correction_factor | number | default 0.4 | Fraction of the excess weight added to IBW; 0.4 is standard, some protocols use 0.3. Range: ≥ 0.2, ≤ 0.5 |
Outputs
| Output | Type | Unit | Description |
|---|---|---|---|
ideal_body_weight_kg | number | kg | 50 kg (male) or 45.5 kg (female) + 2.3 kg per inch over 5 ft. |
percent_of_ideal | number | % | weight_kg / IBW × 100. |
adjusted_body_weight_kg | number | kg | IBW + factor × (actual − IBW). |
adjusted_weight_applies | boolean | True when actual weight exceeds 120% of ideal. | |
dosing_weight_kg | number | kg | Adjusted weight when it applies, otherwise actual weight. |
weight_basis | string | Which weight the suggestion uses and why. |
Example
Male, 175 cm, 100 kg: {"sex":"male","height_cm":175,"weight_kg":100} → {"ideal_body_weight_kg":70.5,"percent_of_ideal":141.9,"adjusted_body_weight_kg":82.3,"adjusted_weight_applies":true,"dosing_weight_kg":82.3}
Female, 160 cm, 60 kg: {"sex":"female","height_cm":160,"weight_kg":60} → {"ideal_body_weight_kg":52.4,"percent_of_ideal":114.5,"adjusted_weight_applies":false,"dosing_weight_kg":60}
GET https://tttkmbb.com/api/v1/calculate/adjusted-body-weight?sex=male&height_cm=175&weight_kg=100
Machine access
- API:
GET https://tttkmbb.com/api/v1/calculate/adjusted-body-weight(query parameters) orPOSTwith a JSON body{"inputs": {...}} - Schema: https://tttkmbb.com/api/v1/calculators/adjusted-body-weight · Markdown: https://tttkmbb.com/medical/adjusted-body-weight.md · JSON definition: https://tttkmbb.com/medical/adjusted-body-weight.json
- MCP: server
https://tttkmbb.com/mcp, toolrun_calculator with calculator_id="adjusted-body-weight" - OpenAPI operationId:
calculate_adjusted_body_weight - Freshness:
static. Authentication: none. Rate limit: fair use (see rate limits).
Sources
- Pai MP, Paloucek FP (2000) The origin of the 'ideal' body weight equations, Ann Pharmacother 34:1066-1069 (peer_reviewed)
- Winter MA et al. (2012) Impact of various body weights and serum creatinine concentrations on the bias and accuracy of the Cockcroft-Gault equation, Pharmacotherapy 32:604-612 (peer_reviewed)
FAQ
Why 120% of ideal?
Below that, the difference between actual and adjusted weight is small; most references (and the Winter 2012 analysis) start using adjusted weight around 120–130% of IBW.
What if actual weight is below ideal?
Actual weight is used for dosing; the adjusted-weight formula is not meant for underweight patients.
Related calculators
- Ideal Weight Calculator — Ideal weight by Devine, Robinson, Miller and Hamwi.
- Creatinine Clearance Calculator — Cockcroft-Gault with adjusted weight.
- BMI Calculator — Weight classification for the same height and weight.