Ideal Body Weight Formulas Explained — Devine, Robinson, Hamwi & Miller Compared

Long before BMI became the standard screening tool, clinicians used a handful of formulas to estimate a single “ideal body weight” figure — originally for calculating medication dosages, not as personal weight targets. Four formulas are still commonly referenced today. Here’s exactly how each one works, how they compare, and why they don’t always agree with each other.

Why These Formulas Exist

Ideal body weight (IBW) formulas were developed to give clinicians a quick estimate of a “typical” healthy weight for a given height, mainly to help calculate accurate medication doses — many drugs are dosed relative to body weight, and using someone’s actual weight can be inaccurate in cases of significant obesity or very low body weight. They were never intended as personal weight-loss goals, though they’re often used informally that way today.

The Four Formulas, With Exact Equations

All four use the same structure: a base weight at 5 feet (60 inches) tall, plus an incremental amount for every inch above that height.

Worked Example: 5’8″ (68 inches)

For a man at 5’8″ (8 inches over the 5-foot base):

The four formulas land within about 5 lb of each other for this height — close, but not identical, which is exactly why none of them should be treated as a single “correct” answer.

Why These Don’t Replace a BMI-Based Range

Every formula above produces a single point estimate, not a range, and none of them account for muscle mass, frame size, or body composition. For everyday personal use, the BMI-based healthy weight range (18.5–24.9 kg/m²) is generally more practical, because it acknowledges that a healthy weight spans a range rather than one exact number. We cover that range by height in our ideal weight for women and ideal weight for men guides.