Ideal Weight Calculators: Why the Formulas Disagree (and What to Use Instead)
Type your height into four different "ideal weight" calculators and you'll get four different answers — sometimes a gap of five kilograms or more. That's not a bug in any one of them. Each formula was built decades ago from a different population for a different purpose, and none of them were ever meant to define a single correct weight for every person of a given height.
The short version
- Every "ideal weight" formula is a linear estimate from height alone — none account for muscle, frame, or body composition.
- Devine (1974) is the most widely used, mainly because it became the default for drug dosing, not because it's more accurate for describing health.
- The four common formulas can disagree by 5kg or more for the same height and sex.
- Body fat percentage and waist-to-height ratio tell you more about actual health than any single ideal-weight number.
Where these formulas actually came from
The Devine formula wasn't designed to define healthy weight at all. Dr. B.J. Devine published it in 1974 to estimate "ideal body weight" for calculating drug dosages — many medications need to be dosed relative to lean tissue rather than total weight, and clinicians needed a fast bedside estimate without access to body composition equipment. It was never validated as a target for general health, but it became so widely used in medicine that it's now the default "ideal weight" formula almost everywhere, including fitness calculators that have nothing to do with drug dosing.
The other three formulas have similarly narrow origins. Robinson (1983) and Miller (1983) were both refinements aimed at improving on Devine for clinical dosing purposes. Hamwi (1964) predates all of them and was developed as a quick rule of thumb for dietitians estimating calorie needs, not as a definition of ideal health.
The four formulas compared
| Formula | Year | Male base + per inch over 5ft | Female base + per inch over 5ft |
|---|---|---|---|
| Devine | 1974 | 50kg + 2.3kg | 45.5kg + 2.3kg |
| Robinson | 1983 | 52kg + 1.9kg | 49kg + 1.7kg |
| Miller | 1983 | 56.2kg + 1.41kg | 53.1kg + 1.36kg |
| Hamwi | 1964 | 48.0kg + 2.7kg | 45.5kg + 2.2kg |
Notice the structure is identical across all four: a base weight for exactly 5 feet tall, plus a fixed amount for every inch above that. The only differences are which base and which per-inch rate each author chose — there's no deeper science distinguishing them, which is exactly why FitCalc's calculator shows the full range rather than picking one and presenting it as definitive.
What every one of these formulas gets wrong
All four share the same blind spots, because they're built the same way:
- No account for muscle mass. A bodybuilder and a sedentary person of the same height get the same "ideal weight" — one of them will exceed it substantially while being leaner and healthier.
- No account for frame size. Wrist or elbow breadth affects how much a person "should" weigh at a given height, and none of these formulas measure it.
- Old, narrow populations. Several were derived from specific hospital or clinical populations decades ago, not broad, representative samples of healthy adults.
- A single number, not a range. Real healthy weight varies enormously between individuals of the same height — collapsing that into one figure was always a simplification for a specific clinical use case, not a health target.
A better lens than a single number
If the goal is actually understanding your health rather than matching an old dosing formula, three things tell you more than ideal weight ever could:
- BMI — a quick screening range (18.5–24.9) rather than a point figure, which at least acknowledges that healthy weight is a band, not a single number.
- Body fat percentage — tells you what your weight is actually made of, which is the piece ideal weight formulas can't see at all.
- Waist-to-height ratio — keeping your waist under half your height is a simple, well-supported marker of cardiometabolic risk that doesn't require any formula at all.
Used together, these give a far more complete picture than any ideal-weight number on its own — and none of them require pretending that a 1974 drug-dosing equation was designed to tell you whether you're healthy.
How to actually use this number
Treat the figure FitCalc shows as a loose historical reference point, not a target. It can be a useful sanity check if a number comes back wildly outside the range — but if you train regularly and sit above every formula on this page while your body fat percentage is in a healthy range, the formulas are wrong for you, not the other way around.
Tools that measure what these formulas can't
FitCalc earns a small commission on purchases made through these links, at no extra cost to you. As an Amazon Associate we earn from qualifying purchases.
-
Body measuring tapeView on Amazon
Waist circumference and waist-to-height ratio need nothing more than a tape measure, and they tell you more about health risk than an ideal-weight number ever will.
-
Body composition scaleView on Amazon
A scale that estimates body fat percentage gives you the piece these height-only formulas are structurally unable to measure.
See where you fall across all four formulas at once.
Open the ideal weight calculator →Frequently asked questions
What comes up most often about ideal weight formulas.
Which ideal weight formula is most accurate?
None of them are more "accurate" than the others in any meaningful sense — they're all linear estimates based on height and sex alone, fitted to different populations decades ago. Devine (1974) is the most widely used in clinical practice, mainly because it became the default for drug dosing calculations, not because it was proven superior for describing healthy weight.
Why is my "ideal weight" lower than my actual healthy weight?
These formulas were built from height alone and have no way to account for muscle mass. A muscular or athletic person will typically weigh more than their formula-based ideal weight while carrying a healthy, even low, body fat percentage. If you train regularly, treat this number as informational rather than a target.
Should I try to reach my ideal weight exactly?
No. Treat it as a loose reference point rather than a goal. Body fat percentage, waist circumference, how your clothes fit, and how you feel and perform are all more informative than matching a decades-old formula based on height alone.
Is ideal weight the same as a healthy BMI weight range?
They're related but calculated differently. BMI-based healthy weight range comes from the WHO's 18.5–24.9 BMI band applied to your height. Ideal weight formulas like Devine produce a single point figure from a different, older set of equations. They usually land in a similar area but rarely match exactly.
Do these formulas work for children?
No. All four formulas were derived from adult populations and assume adult body proportions. Healthy weight for children and teenagers is assessed using age- and sex-specific growth charts instead, not adult ideal weight equations.
What should I use instead of an ideal weight number?
A combination usually tells you more: a BMI range for a rough screen, body fat percentage or waist-to-height ratio for actual composition, and your own trend over time. None of these replace ideal weight formulas so much as answer the more useful questions those formulas can't.
This guide is for general education purposes and isn't medical advice. Healthy weight varies by individual, medical history, and body composition — speak to a doctor or registered dietitian about what's right for you.