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.