Many calculations in medicine and nutrition scale with body weight, from the dose of a drug to the number of calories a patient should receive. For most people actual weight works well. When someone is heavy for their height, though, extra fat tissue behaves differently from lean tissue: it holds less water, receives less blood flow and uses less energy. Using full weight can then overestimate how much of a drug is needed or how many calories are burned. Adjusted body weight is the compromise. It starts at the ideal body weight for the person’s height and adds a fraction of the excess.
This calculator computes ideal body weight with the Devine formula and then applies a 0.4 or 0.25 correction factor to the difference. It is an educational tool; medicine doses must come from a clinician.
How to use the adjusted body weight calculator
- Select sex and enter height. Devine’s formula has different bases for men and women.
- Enter actual weight.
- Choose the correction factor. 0.4 is the conventional value for dosing some antibiotics, and 0.25 is used in some nutrition formulas.
- Read ideal weight, adjusted weight and how far above ideal you are. If your weight is at or below ideal, no adjustment applies.
Adjusted body weight formula
Adjusted body weight = IBW + factor × (actual weight − IBW)
Percent of ideal = actual weight ÷ IBW × 100
Ideal weight is from Devine BJ, Drug Intelligence and Clinical Pharmacy 1974;8:650–655. The idea of an adjusted weight for obese patients and the use of a 0.4 factor are described in the clinical pharmacy literature, reviewed in Pai MP, Paloucek FP, Ann Pharmacother 2000;34:1066–1069. Use of a 25 percent factor for energy estimates in obese patients is discussed by Krenitsky J, Nutr Clin Pract 2005;20:468–473.
Worked example
A man who is 178 cm (70.08 in) tall and weighs 120 kg.
- Inches over 60: 10.08. Devine IBW = 50 + 2.3 × 10.08 = 73.2 kg
- Excess weight = 120 − 73.2 = 46.8 kg (164% of ideal)
- Adjusted body weight = 73.2 + 0.4 × 46.8 = 91.9 kg
- With a 0.25 factor the adjusted weight would be 84.9 kg.
Adjusted weight for sample men
| Height (man) | Actual weight | Ideal weight (Devine) | Adjusted weight (factor 0.4) | Actual as % of ideal |
|---|---|---|---|---|
| 160 cm | 90 kg | 56.9 kg | 70.1 kg | 158% |
| 160 cm | 110 kg | 56.9 kg | 78.1 kg | 193% |
| 160 cm | 130 kg | 56.9 kg | 86.1 kg | 229% |
| 170 cm | 90 kg | 65.9 kg | 75.6 kg | 136% |
| 170 cm | 110 kg | 65.9 kg | 83.6 kg | 167% |
| 170 cm | 130 kg | 65.9 kg | 91.6 kg | 197% |
| 180 cm | 90 kg | 75.0 kg | 81.0 kg | 120% |
| 180 cm | 110 kg | 75.0 kg | 89.0 kg | 147% |
| 180 cm | 130 kg | 75.0 kg | 97.0 kg | 173% |
| 190 cm | 90 kg | 84.0 kg | 86.4 kg | 107% |
| 190 cm | 110 kg | 84.0 kg | 94.4 kg | 131% |
| 190 cm | 130 kg | 84.0 kg | 102.4 kg | 155% |
Why a correction is used
- Drug distribution. Water-soluble drugs distribute mostly into lean tissue and extracellular fluid, so dosing by total weight can overshoot in obesity.
- Energy use. Fat mass uses much less energy than lean mass per kilogram, so calorie estimates from full weight run high.
- Imperfect proxies. A single correction factor cannot capture each person’s body composition; hence different factors for different purposes.
Cautions
Ideal weight formulas assume average body composition and were not designed to define a healthy weight; see the Ideal Weight Calculator for the context. Muscular people can have a high actual-to-ideal ratio without excess fat. BMI (37.9 in the example) and body composition measures such as the Lean Body Mass Calculator give additional information, and the Body Surface Area Calculator covers another weight-based measurement used in clinical dosing. For calorie planning use the Calorie Calculator. Never adjust a prescribed dose yourself.
This page is for information only and is not medical or dietary advice. Speak to a doctor or registered dietitian before starting a weight-loss plan, especially if you have a medical condition, take medicines, are pregnant or have a history of disordered eating.
Sources
- Devine BJ. Gentamicin therapy. Drug Intelligence and Clinical Pharmacy 1974;8:650–655.
- Pai MP, Paloucek FP. The origin of the “ideal” body weight equations. Ann Pharmacother 2000;34:1066–1069.
- Krenitsky J. Adjusted body weight, pro: evidence to support the use of adjusted body weight in calculating calorie requirements. Nutr Clin Pract 2005;20:468–473.
Frequently asked questions
What is adjusted body weight?
Adjusted body weight (ABW) is a corrected weight used for people whose actual weight is well above their ideal weight. It adds a fraction of the excess weight to the ideal weight: ABW = IBW + factor × (actual − IBW). The idea is that excess fat tissue is not as metabolically active as lean tissue, so using full weight overestimates needs.
Where is adjusted body weight used?
Mostly in healthcare. Pharmacists and doctors use it to dose some medicines, notably certain antibiotics, in patients with obesity, and dietitians use versions of it when estimating calorie needs. The choice of factor depends on the purpose.
Which correction factor should I use?
A factor of 0.4 is traditional for dosing aminoglycoside antibiotics; some nutrition references use 0.25 for estimating energy needs in obesity. These are conventions, and the right choice depends on the clinical situation. Ask your clinician rather than choosing yourself.
Can I use this to dose my own medicine?
No. This tool is for information and education. Drug doses must be decided by a doctor or pharmacist who knows your medical history, kidney function and the specific medicine.
Why does it use the Devine formula?
Devine’s 1974 equation is the most widely used ideal body weight formula in clinical practice, especially for dosing. See the Ideal Weight Calculator for the other formulas.