What "Ideal Weight" Formulas Actually Estimate
Ideal body weight formulas were originally developed decades ago, primarily for clinical purposes like estimating appropriate medication dosages based on body size, not as a definitive personal health target for the general public to aim for. Several different formulas exist — Devine, Robinson, Miller, Hamwi are among the most commonly cited — each producing a somewhat different estimate from the same height input, which itself is a useful reminder that "ideal weight" is more of an estimated reference range than a single precise, universally agreed number.
The Devine Formula
Men: IBW = 50 kg + 2.3 kg × (height in inches over 60)
Women: IBW = 45.5 kg + 2.3 kg × (height in inches over 60)
Originally developed in 1974 specifically to help estimate drug dosages for clinical purposes, the Devine formula remains widely referenced today despite its clinical origin, often used more broadly as a general reference point than its original narrow medical purpose intended. It uses height as the primary variable, with separate baseline constants for men and women reflecting typical physiological differences.
Why Different Formulas Give Different Answers
Each ideal weight formula was developed using different reference populations and different underlying assumptions about the height-weight relationship, which is why running the same height through Devine, Robinson, Miller, and Hamwi formulas typically produces a range of results rather than one single consistent number — sometimes differing by several kilograms between formulas for the identical height input. This variation itself is informative: it demonstrates that "ideal weight" was never meant to be a single precise number, but rather a reasonable estimated range, and seeing several formulas converge on a broadly similar range provides more useful context than fixating on any one formula's specific output as a precise target.
Limitations Worth Understanding
These formulas share a significant limitation with BMI — they're based purely on height, with gender as the only other input, meaning they can't account for body composition, frame size, muscle mass, or other individual factors that genuinely affect what a healthy weight looks like for a specific person. A muscular athlete will often show a calculated "ideal weight" well below their actual healthy weight, since the formula has no way to account for their higher muscle mass. Similarly, someone with a naturally larger or smaller bone structure than the reference population these formulas were developed from may see a calculated ideal weight that doesn't genuinely reflect a healthy target for their specific frame. These formulas are best understood as one general reference point among several, not a definitive personal target that overrides individual context.
A More Useful Framing: A Healthy Range, Not a Single Number
Rather than fixating on a single calculated "ideal weight" figure, it's generally more useful to think in terms of a healthy weight range — often informed by BMI's normal weight category (18.5-24.9) applied to your specific height, cross-referenced against how several different ideal weight formulas cluster for the same height, and layered with your own awareness of your body composition, frame, and how you feel and function at different weights within that general range. This range-based framing better reflects the genuine individual variation in what a healthy weight actually looks like across different people of the same height, rather than implying there's one single correct number everyone of a given height should aim for.
When These Formulas Are Genuinely Useful
Despite their limitations for personal goal-setting, these formulas retain genuine clinical utility in specific contexts — medication dosing calculations in healthcare settings, nutritional assessment frameworks, and as one input among several in broader health evaluations conducted by medical professionals who understand how to interpret the result alongside other relevant individual factors. For general personal awareness, they're most useful as a rough reference point to discuss with a doctor if you're genuinely uncertain about a healthy weight target for your specific situation, rather than as a number to pursue rigidly on your own without broader context.
How to Use This Calculator
Enter your height and gender to see an estimated ideal weight range based on commonly used formulas. Treat the result as a general reference point rather than a precise personal target, and consider discussing a genuinely appropriate healthy weight goal with a doctor who can factor in your individual body composition, frame, and overall health context.
A Worked Example Comparing Formulas
Consider a woman standing 165 cm (about 65 inches) tall. Using the Devine formula: 45.5 + 2.3 × (65-60) = 45.5 + 11.5 = 57 kg. The Robinson formula, another commonly cited approach, might produce a slightly different figure — often within a kilogram or two of Devine for typical heights, though the exact gap varies. The Hamwi formula, yet another approach, might land somewhere in a similar general range as well. Rather than treating any single one of these as the definitive correct answer, the more useful takeaway is that all three cluster within a roughly similar range — in this case, likely somewhere around 55-60 kg — providing a reasonable general reference band rather than one precise number to target exactly.
Ideal Weight and Body Frame Size
Some more refined approaches to ideal weight estimation incorporate an adjustment for body frame size — small, medium, or large — typically estimated through wrist circumference relative to height, acknowledging that two people of identical height can have genuinely different healthy weights due to differing bone structure and frame size. A large-framed individual carrying a weight above a standard formula's output isn't necessarily unhealthy, just built on a larger overall frame, while a small-framed individual might have a genuinely healthy weight below what a frame-agnostic formula suggests. This is one more reason to treat basic height-and-gender-only formulas as a starting reference rather than a precise, universally applicable target, since frame size is a real, individually variable factor these simpler formulas don't capture.
Ideal Weight Formulas vs BMI: Two Different Approaches to a Similar Question
Ideal weight formulas and BMI both attempt to provide a general reference for healthy body weight, but they approach the question somewhat differently. BMI expresses a range (18.5-24.9 for "normal") applicable across any height, requiring you to calculate what weight range that translates to for your specific height. Ideal weight formulas instead calculate a specific point estimate (or narrow range across formulas) directly from height. Both share similar fundamental limitations — neither accounts for body composition, muscle mass, or frame size — but using them together, checking whether your weight falls within BMI's normal range and roughly aligns with clustered ideal weight formula outputs, provides a bit more triangulated context than relying on either single approach alone, even though neither method individually captures the full picture of what constitutes a genuinely healthy weight for any specific individual.
The Historical Context Behind These Formulas
Many commonly used ideal weight formulas trace back to insurance industry data from the mid-20th century, originally developed by life insurance companies analyzing mortality data across different height-weight combinations to help set policy pricing — a somewhat different original purpose than personal health guidance, though the underlying height-weight-mortality relationships these historical datasets captured have informed much of modern weight-related health guidance since. Understanding this historical origin helps explain both why these formulas exist in their current form and why they carry certain limitations — they were built from population-level mortality data from a specific historical period and demographic, not from a comprehensive modern understanding of individual body composition and health that more sophisticated modern health assessment tools now incorporate.