What should I weigh? The honest answer is a range
Four ideal-weight formulas give four different answers for the same person, and none was designed for the question you are asking.
CalculatorHealthy Weight RangeOpen →Type your height into an ideal weight calculator and you will get a confident number. Type it into a different one and you will get a different confident number. The gap between them is frequently five kilograms or more.
That disagreement is not a bug in the calculators. It is the honest answer to the question.
Where the formulas actually came from
The four equations that appear in almost every ideal-weight calculator — Devine, Robinson, Miller and Hamwi — share an origin that surprises most people who use them.
They come from clinical practice, not from health research — though the specific purpose varies more than the popular version of this story admits. Devine’s equation was devised for drug dosing: some medications must be dosed on lean body size rather than total weight, and clinicians needed a quick bedside estimate of what a patient of a given height would weigh without excess fat. Hamwi’s, by contrast, came out of dietary planning for people with diabetes. Behind all of them sits an older lineage of actuarial height-weight tables built from life-insurance policyholder data collected around the turn of the twentieth century.
What they share is more important than what separates them. Work tracing the history of these equations found they were built on limited data and refined largely by convention rather than by rigorous derivation. 1
None of them was intended to answer “what should I weigh to be healthy”, and none carries any information about muscularity, frame size, or body composition. A muscular person will read as well above their “ideal” weight while being nothing of the sort.
What BMI is and is not for
BMI gets more criticism than it deserves and more use than it warrants, which is an unusual combination.
As a population screening tool it is defensible. It is cheap, requires no equipment, and correlates well enough with body fatness across large groups to be useful in epidemiology. Public health bodies use it for exactly this reason.
Its failure mode is individual application at the extremes. It cannot distinguish muscle from fat, so it misclassifies muscular people as overweight and can miss excess fat in people with low muscle mass — the second error being the more clinically concerning of the two, and the one that gets far less attention.
A critical review of the measure puts it plainly: BMI has been useful in population studies, but it is a poor indicator of percent body fat and carries no information about where that fat sits on the body. 3
The reasonable position is neither “BMI is meaningless” nor “BMI defines your health”. It is a crude screening instrument that works acceptably in aggregate and poorly at the tails.
The better single number
If you take one measurement from this article, take waist-to-height ratio.
Divide your waist circumference by your height in the same units. Below 0.5 is the commonly cited threshold. Reviews comparing screening tools have found waist-to-height performs better than BMI or waist circumference alone for identifying cardiometabolic risk — a meta-analysis of more than 300,000 adults found it improved discrimination over BMI by four to five per cent, against three per cent for waist circumference. 4
Three things make it attractive. It requires one tape measurement rather than an estimate, so it carries almost none of the error that plagues body-fat methods. It captures central adiposity specifically, which is the fat distribution most associated with metabolic risk. And the threshold is easy to remember: keep your waist under half your height.
Choosing a target that makes sense
Start with the healthy-BMI band, not a point. For most heights that band spans fifteen to twenty kilograms. Somewhere in that range is defensible; the exact figure is preference and context.
Adjust upward if you carry muscle. If you train seriously, expect to sit above what the formulas suggest, and treat that as expected rather than as a problem to solve.
Use composition, not just weight. Two people at the same weight with a ten-point body-fat difference are in very different situations. Our body fat and FFMI tools address the question weight alone cannot.
Set a behaviour target, not only an outcome. “Reach 78 kilograms” is a target you do not directly control. “Hit my protein target and train three times a week” is one you do, and it tends to produce the first anyway.
The bottom line
There is no single correct weight for a given height, and the confident numbers produced by ideal-weight calculators come from equations built for a different purpose entirely.
Use the healthy-BMI band as a broad orientation, waist-to-height as your most reliable single risk indicator, and body composition to answer the questions weight alone cannot. Then judge progress by how you look, perform and feel over months — not by proximity to a formula from 1974.
- Pai MP, Paloucek FP. The origin of the ideal body weight equations. Ann Pharmacother, 2000;34(9):1066-1069.Checked against the original
- Ashwell M, Gibson S. Waist-to-height ratio as an indicator of early health risk. BMJ Open, 2016.Checked against the original
- Nuttall FQ. Body mass index: obesity, BMI, and health: a critical review. Nutr Today, 2015;50(3):117-128.Checked against the original
- Ashwell M, Gunn P, Gibson S. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: systematic review and meta-analysis. Obes Rev, 2012;13(3):275-286.Checked against the original
How we reviewed this article
Every factual claim here is sourced to peer-reviewed research, a government or institutional guideline, or a named textbook. Where a claim carries a numbered marker, it links straight to that source below, so you can check the original rather than take our word for it.
This article has not been reviewed by a credentialed professional. It was researched and written from the primary sources listed below, but a reviewer catches things citations cannot — omitted contraindications, misread effect sizes, and questions of emphasis. We would rather tell you that than imply a review that did not happen. This article touches on health risk, so treat its claims as general information and raise anything that applies to you with a clinician.
Written and edited by a person. All 4 citations have been opened and checked against the original — that the source exists, and that it supports the specific claim it is attached to.
We revisit articles as the evidence changes. This one was last updated on August 20, 2026. Spotted an error? Tell us — corrections are logged publicly.
Estimates and general guidance only. This is not medical advice.
- The healthy-weight tool previously produced results from an incomplete form — clearing the weight field returned a BMI category of "Underweight" and goal weights calculated from a height of zero. It now waits for both measurements before showing anything.
- Added a caveat wherever a BMI or body-fat category is shown, noting that these bands come from population averages and cannot distinguish muscle from fat.
- All calculators now state that they are built for adults aged 18 and over. The equations behind them were developed and validated on adult bodies and do not produce meaningful results for anyone still growing.