Understanding the Ideal Body Weight (IBW) Formulas
The concept of "Ideal Body Weight" was originally developed by the insurance industry in the mid-20th century to associate height and weight with mortality rates. Later, medical professionals adapted these charts into mathematical formulas to safely prescribe medications that require strict dosing based on body mass.
Are these formulas right for you? If you are completely sedentary, these equations provide a reasonable estimate of a healthy body weight. If you actively lift weights or play sports, you will easily exceed these weights while remaining lean and healthy. Muscle weighs more than fat by volume.
The Three Primary IBW Equations
1. The Devine Formula (1974)
Dr. Ben Devine originally created this formula strictly to determine the correct dosage of certain drugs (like gentamicin) in obese patients. Because it proved so easy to use, it quickly became the default medical standard for estimating general ideal body weight.
- Men: 50.0 kg + 2.3 kg per inch over 5 feet
- Women: 45.5 kg + 2.3 kg per inch over 5 feet
2. The Robinson Formula (1983)
Dr. J.D. Robinson published an update to the Devine formula because he found that Devine often underestimated ideal weight for shorter women and men. Robinson's update provides a slightly modified scaling factor.
- Men: 52.0 kg + 1.9 kg per inch over 5 feet
- Women: 49.0 kg + 1.7 kg per inch over 5 feet
3. The Miller Formula (1983)
Published in the same year as Robinson, Dr. Miller proposed another variation. The Miller equation uses a lower baseline weight but adds weight at a more conservative rate as height increases.
- Men: 56.2 kg + 1.41 kg per inch over 5 feet
- Women: 53.1 kg + 1.36 kg per inch over 5 feet
Frequently Asked Questions
Why do the different formulas give me different answers?▼
Because there is no biological law that dictates exactly what a human should weigh. These are statistical models created by different doctors at different times. The average of all three usually provides the most realistic baseline target.
What if I am shorter than 5 feet?▼
These classic formulas were designed exclusively for adults 5 feet and taller. If you are under 5 feet, the math breaks down and often deducts weight at an overly aggressive rate. In medical settings, alternative pediatric or specialized formulas are used for individuals under 60 inches.
How is Ideal Weight different from BMI?▼
BMI (Body Mass Index) provides a broad range of acceptable weights based on height (e.g., a BMI of 18.5 to 24.9). Ideal Body Weight formulas output a single, specific numerical target. Both fail to account for body composition (muscle vs. fat).
