Ideal Body Weight Formulas: History Explained

Fact-checked against peer-reviewed sources. Last updated: September 30, 2026.

Ideal body weight formulas show up on nearly every fitness site as though they were designed to tell you your best weight. They weren't. Their real origin explains why they're a poor fit for that job today.

Built for Drug Dosing, Not Fitness

The Devine formula, the most widely cited of the group, was published in 1974 specifically to help clinicians estimate drug dosages for medications where dosing needed to scale with body size, not fat mass specifically. Several anesthesia and pharmacology drugs distribute through lean tissue rather than fat, so an estimate of "lean-ish" body weight was clinically useful for calculating a safe dose.

The Hamwi formula predates it, from 1964, built for even quicker bedside estimates in clinical settings. Robinson and Miller, both published in 1983, were attempts to refine Devine's numbers using updated population data, not fundamentally different formulas.

None of the four were built by studying what body weight correlates with optimal health, athletic performance, or aesthetics. They were built to answer a narrower clinical question: roughly how much does a "normal-sized" person of this height weigh, for dosing purposes.

Why That Origin Story Matters Today

Because these formulas use height as the only input, they cannot distinguish between a heavily muscled athlete and a sedentary person of the same height. Both get assigned the identical "ideal" weight, despite potentially very different body compositions and health profiles.

A 180 cm bodybuilder at 95 kg with 10% body fat is carrying a healthy, high amount of muscle. The same person's Devine IBW calculates to about 75 kg, a number that would represent significant, unwanted muscle loss if actually pursued.

Formula Comparison

What Replaced IBW in Modern Practice

Clinical and fitness practice has largely moved toward body composition metrics that account for what IBW formulas miss:

• BMI (despite its own well-documented limitations) at least incorporates actual current weight, not just height
• Body fat percentage, measured or estimated, directly addresses what IBW formulas can't see
• Waist-to-height ratio is increasingly used as a simple screen for metabolic health risk, since it reflects fat distribution rather than total mass

A More Useful Question Than "What's My IBW?"

For body composition goals, a more useful framing than "what should I weigh" is "what body fat percentage am I aiming for, and what would my weight look like at that body fat given my current or target lean mass." That calculation runs through lean body mass, not height alone. See our Lean Body Mass Calculator for that approach.

Frequently Asked Questions

Are IBW formulas still used in medicine today?

Yes, still commonly used for calculating drug dosages in clinical settings, which is the purpose they were actually built for. Their use as a personal fitness target is a repurposing, not their original intent.

Why do the four formulas give different numbers for the same height?

Each was derived from a different population sample and used slightly different statistical methods. The differences between them (typically a few kilograms) reflect that variation, not one being more "correct" than another.

Should athletes ignore IBW numbers entirely?

For body composition goals, yes, largely. IBW cannot account for muscle mass. An athlete's target weight is better derived from a desired body fat percentage combined with their actual or goal lean body mass.

Sources

• Devine BJ. "Gentamicin therapy." Drug Intelligence and Clinical Pharmacy, 1974 (original IBW formula, developed for drug dosing).
• Robinson JD, Lupkiewicz SM, Palenik L, et al. "Determination of ideal body weight for drug dosage calculations." American Journal of Hospital Pharmacy, 1983. PubMed search