Type your height into four different "ideal weight" formulas and you'll get four different numbers — sometimes a meaningful gap between them. That's not a bug in any one formula; it's a direct result of how and why these formulas were originally created.
Where These Formulas Actually Came From
The Devine (1974), Robinson (1983), Miller (1983), and Hamwi (1964) formulas are all decades old, and several were originally developed to support medical dosing calculations — estimating a patient's weight for drug dosage purposes — rather than as general fitness or wellness targets. They've since been adopted much more broadly than their original clinical purpose, which is part of why people are often surprised at how simple the underlying math actually is: a base value plus a fixed increment for every inch of height above five feet.
Why Four Formulas Give Four Different Numbers
Each formula was built independently, using its own reference population and its own assumptions about the relationship between height and a "typical" or "ideal" weight. Different source data naturally produces different coefficients, so the same height plugged into all four will land in a range rather than a single agreed-upon number. That range is informative in its own right — it shows you how much these estimates can vary even among formulas that are all considered legitimate reference points.
What None of These Formulas Measure
All four formulas take only height and gender as inputs. None of them account for muscle mass, bone density, frame size, or body composition — two people of the same height and gender can have very different healthy weights depending on build. That's why these numbers work best as a rough starting reference rather than a personalized target, and why they're not a substitute for an actual medical assessment.
Ideal Weight vs. BMI: Not the Same Question
Body Mass Index and "ideal weight" formulas often get mentioned in the same breath, but they answer different questions. BMI is a ratio calculated from your actual height and weight together, with no reference population involved in the calculation itself. Ideal weight formulas work the other direction — starting only from height, they output a single suggested weight based on data from a specific historical population. The two often land in a similar general range, but mechanically they're different calculations.
Calculate Your Estimate Instantly
See all four formulas' estimates side by side for your own height with our free Ideal Weight Calculator.
FAQ
Which formulas does this use? The Devine, Robinson, Miller, and Hamwi formulas — four different published medical formulas from the 1960s–80s that are still commonly referenced today, each with a slightly different result since they were derived from different population studies.
Why do the formulas give different results? Each was developed independently, often originally for medical dosing calculations rather than general fitness, using different reference populations — the spread between them is a useful reminder that "ideal weight" is an estimate, not a precise medical target.
Is this a substitute for medical advice? No — these formulas don't account for muscle mass, body composition, frame size, or individual health conditions. Use this as a general reference point only, not a diagnosis or medical recommendation.
Is ideal weight the same thing as a healthy BMI? No — BMI is a ratio calculated purely from height and weight, with no reference population baked in, while these ideal weight formulas instead output a single target weight derived from height alone. They're two different calculations that often point in a similar general direction, but they aren't measuring the same thing.