Ideal Body Weight (IBW) Calculator

Ideal body weight (IBW) is a reference weight derived from your height and sex. It is used every day in medicine, to dose drugs such as aminoglycosides, to set ventilator tidal volume in millilitres per kilogram of IBW, and to normalise creatinine clearance, because dosing on a very heavy patient's actual weight can overshoot. All four formulas on this page share the same shape:

IBW = base + perInch × n, where n = (height in inches) − 60

The height is first converted from centimetres to inches (dividing by 2.54), then 60 inches, five feet, is subtracted to get n, the number of inches over five feet. Each formula plugs its own base weight and per-inch increment into that equation:

• Devine (1974): male 50 + 2.3n · female 45.5 + 2.3n
• Robinson (1983): male 52 + 1.9n · female 49 + 1.7n
• Miller (1983): male 56.2 + 1.41n · female 53.1 + 1.36n
• Hamwi (1964): male 48 + 2.7n · female 45.5 + 2.2n

Devine is flagged as the dosing standard because most dosing research and guidelines are built on it. The tool also computes the WHO healthy weight range by evaluating weight = BMI × height² at BMI 18.5 and 24.9, giving a low–high band in kilograms for your height.

When you enter an actual weight, two more numbers appear. Adjusted body weight (ABW) = IBW + 0.4 × (actual − IBW), using the Devine IBW; the 0.4 factor reflects the fraction of excess weight that is metabolically active. Percent of IBW is actual ÷ IBW × 100. Clinical convention then picks the dosing weight: actual weight when you are at or below IBW, IBW between there and 120% of IBW, and ABW at or above 120%. These rules and the 0.4factor are set out in Pai & Paloucek's review of the ideal-weight equations. Every Devine value is cross-checked against the equivalent metric form of the equation, so the centimetre-to-inch step is verified internally.

• Pai MP, Paloucek FP. The origin of the “ideal” body weight equations. Ann Pharmacother. 2000;34:1066–1069
• Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655 (origin of the Devine equation)
• Robinson JD, et al. Determination of ideal body weight for drug dosage calculations. Am J Hosp Pharm. 1983;40:1016–1019
• World Health Organization: Body mass index (healthy range 18.5–24.9 kg/m²)

The formulas and constants on this page were last cross-checked against these sources on 2026-07-16. This tool is for education and general reference only; it does not replace advice from a doctor or pharmacist, and drug doses must always be confirmed by a qualified clinician.