What Is an Ideal Weight Calculator?
An ideal body weight (IBW) calculator estimates the weight range considered healthy for a person of a given height and sex. Unlike BMI, which measures weight relative to height on a continuous scale, IBW formulas produce a single target number derived from clinical research. Physicians and dietitians use IBW to guide medication dosing, nutritional planning, and fitness goal-setting. While no single number can define health for every individual, IBW provides a practical starting point for conversations about weight management.
The Science Behind the Formulas
Several competing formulas have been developed over the decades, each with a slightly different approach. Understanding the differences helps you choose the most relevant estimate for your situation.
Hamwi Formula (1964)
Developed by Dr. G.J. Hamwi for clinical use, this formula is still widely used in hospitals today. For men, it starts at 106 lbs for 5 feet of height and adds 6 lbs per inch above that. For women, it starts at 100 lbs and adds 5 lbs per inch. A 5'10" man would have an IBW of 106 + (10 x 6) = 166 lbs.
Devine Formula (1974)
Originally created to calculate drug dosages, the Devine formula is expressed in kilograms. For men: 50 kg + 2.3 kg per inch over 5 feet. For women: 45.5 kg + 2.3 kg per inch over 5 feet. This formula is the basis for most pharmaceutical dosing guidelines and remains the most widely cited in medical literature.
Robinson Formula (1983)
A refinement of the Devine formula, Robinson's equation uses slightly different constants: Men: 52 kg + 1.9 kg per inch over 5 feet. Women: 49 kg + 1.7 kg per inch over 5 feet. It tends to produce slightly higher estimates than Devine for taller individuals.
How to Use Your Ideal Weight Result
Your IBW result is a reference point, not a strict target. If your current weight is within 10% of your IBW, you are likely in a healthy range. If you are significantly above your IBW, even modest weight loss of 5-10% of your current body weight can produce meaningful health benefits, including reduced blood pressure and improved blood sugar control. If you are below your IBW, consult a healthcare provider, as being underweight carries its own health risks.
Remember that IBW formulas do not account for muscle mass. A competitive athlete may weigh well above their calculated IBW while having an excellent body composition. Always combine IBW with other metrics such as body fat percentage, waist circumference, and overall fitness level for a complete picture of your health.