How to Calculate Ideal Body Weight
Explore the most common ideal body weight formulas including Devine, Robinson, Miller, and Hamwi. Understand which formula to use and how to interpret the results for your health goals.
What Is Ideal Body Weight?
Ideal Body Weight (IBW) is an estimated target weight associated with optimal health outcomes for a given height and sex, originally developed to guide drug dosing in clinical medicine. Unlike BMI, IBW produces a single target weight rather than a range, making it practical for clinical calculations involving medication, anesthesia, and ventilator settings. It is not a cosmetic or aesthetic standard but a clinical approximation of a biologically healthy weight. Multiple formulas exist, each with slightly different assumptions and outputs.
The Devine Formula
The Devine formula, published in 1974, is the most widely used IBW equation in medical settings: For men: IBW (kg) = 50 + 2.3 × (height in inches − 60). For women: IBW (kg) = 45.5 + 2.3 × (height in inches − 60). It was originally derived for predicting tidal volume in respiratory therapy and was never intended as a general health benchmark. Despite its clinical origin, it has become a default reference in pharmacokinetics and critical care.
Other Common IBW Formulas
The Robinson formula (1983) tends to give slightly lower estimates: men: 52 + 1.9 × (height in inches − 60); women: 49 + 1.7 × (height in inches − 60). The Miller formula (1983) gives the lowest values: men: 56.2 + 1.41 × (height in inches − 60); women: 53.1 + 1.36 × (height in inches − 60). The Hamwi formula uses a simpler base: men: 106 lbs for the first 5 feet, plus 6 lbs per additional inch; women: 100 lbs for the first 5 feet, plus 5 lbs per additional inch. Results across formulas can differ by 5–10 kg, illustrating the inherent imprecision of the concept.
Adjusted Body Weight for Obese Patients
In clinical settings, when a patient's actual body weight significantly exceeds their IBW, an Adjusted Body Weight (AdjBW) is often used for drug dosing: AdjBW = IBW + 0.4 × (actual weight − IBW). This correction accounts for the fact that excess adipose tissue is not entirely metabolically inert and does partially distribute some drugs. AdjBW is particularly important for antibiotics, paralytics, and certain chemotherapy agents. Clinicians should always consult pharmacokinetic references, as the appropriate weight scalar varies by drug.
IBW vs. Healthy Weight Ranges
IBW formulas produce a single number, which can be misleading because healthy weight is better understood as a range corresponding to BMI 18.5–24.9. For example, a 5'10" man has an IBW of about 73 kg (Devine), while the healthy BMI range spans 58–79 kg. IBW does not account for frame size, muscle mass, age, or ethnicity. Using IBW as a rigid personal target is not recommended; it is most appropriately used in clinical dosing contexts.
Limitations and Practical Use
All IBW formulas underperform for individuals below 5 feet tall or with very tall stature, as the linear scaling assumptions break down at extremes. They are also derived from population studies of mid-20th century adults and may not reflect modern population diversity or health science. For personal health goals, a target within the healthy BMI range combined with body fat percentage assessment provides a more complete picture. Discuss any specific weight target with a healthcare provider who can account for your full health history.
Try These Calculators
Put what you learned into practice with these free calculators.
Related Guides
How to Calculate BMI (Body Mass Index)
Learn how to calculate BMI using the standard formula for both metric and imperial units. Understand what your BMI score means and its limitations as a health indicator.
How to Calculate Body Fat Percentage
Learn the main methods for calculating body fat percentage, including skinfold calipers, the U.S. Navy method, and DEXA scanning. Understand healthy ranges by age and sex.
How to Calculate Daily Calorie Needs
Find out how to calculate your Total Daily Energy Expenditure (TDEE) using BMR and activity level multipliers. Use this to set accurate calorie goals for weight loss, maintenance, or gain.