Ideal Weight Calculator
Find your ideal body weight based on height and frame size.
Related calculators
About
Ideal Weight Calculator
Almost everyone has tried to lose weight at some point, or knows somebody who has, and most of that effort is aimed at an idea of an ideal body absorbed from television, magazines and social media. Ideal body weight has almost nothing to do with that. It was invented to work out drug doses.
What ideal body weight was actually for
IBW exists because some drugs distribute through lean tissue rather than fat. Dose a heavy patient on total body weight and you can badly overshoot, because the extra weight is largely adipose and the drug never goes there. Ben Devine published his formula in 1974 in a letter about gentamicin dosing, an antibiotic where the gap between a working dose and a toxic one is narrow. Hamwi produced his a decade earlier as a bedside shortcut for planning diabetic diets.
The formulas are still doing that job. Predicted body weight from height and sex is how ventilator tidal volumes are set in intensive care, following the ARDS Network protocol of about 6 millilitres per kilogram. A patient's fat mass does not change the size of their lungs, so the dose follows their frame rather than the scale.
Sport picked the idea up separately, because weight classes need a number. Neither use has anything to do with how a person looks at a given weight, and neither was designed to tell you what to weigh.
Why IBW is not a health target
The formulas take height and sex. That is the entire input. They know nothing about how much of you is muscle, where your fat sits, how old you are, or what your bones weigh. A rugby forward and a sedentary office worker of the same height and sex get the same answer, and for one of them it is nonsense.
This is why fit, healthy athletes routinely come out overweight on IBW and on BMI. It is also why people sitting outside their supposed ideal weight in either direction can be in perfectly good health. Treat the number as a reference point rather than a goal, and treat the habits underneath it as the thing that matters: regular movement, food that mostly started as food, enough sleep.
How much a person should weigh is not settled science. No measure, IBW or BMI or anything else, can state a single correct weight for an individual.
What moves the number
Age
In theory age barely matters once growth stops, around 14 to 15 for girls and 16 to 17 for boys. In practice it does two things. People shrink: men lose about 1.5 inches of height by 70 and women about 2 inches, and shorter height means a lower IBW from the same formula. Lean muscle also declines with age while fat accumulates more readily, so the same weight at 60 is a different body from the same weight at 25. Resistance training, protein intake, sleep and stress management all slow that drift.
Sex
Women generally weigh less than men despite carrying a higher percentage of body fat. Male bodies carry more muscle, which is denser than fat, and higher bone density on top of that. Men are also taller on average. Every one of the four formulas gives women a lower base weight, a lower increment per inch, or both.
Height
Taller people carry more of everything, muscle and fat and bone, so they weigh more. At a matched height a man will typically weigh 10% to 20% more than a woman.
Body frame size
Two people of identical height and sex can have visibly different skeletons, and bone weighs something. Frame size is estimated from wrist circumference relative to height, because the wrist carries almost no fat or muscle to confuse the measurement. Wrap a tape around the smallest part of the wrist, just past the bone on the hand side.
| Women, by height | Small | Medium | Large |
|---|---|---|---|
| Under 5 ft 2 in | under 5.5 in | 5.5 to 5.75 in | over 5.75 in |
| 5 ft 2 in to 5 ft 5 in | under 6 in | 6 to 6.25 in | over 6.25 in |
| Over 5 ft 5 in | under 6.25 in | 6.25 to 6.5 in | over 6.5 in |
| Men, by height | Small | Medium | Large |
|---|---|---|---|
| Over 5 ft 5 in | 5.5 to 6.5 in | 6.5 to 7.5 in | over 7.5 in |
A large-framed person will weigh more than a small-framed one at the same height, and neither IBW nor BMI accounts for it. Enter your wrist measurement above and the calculator will classify your frame alongside the rest of the results.
The four formulas
All four share one shape: a base weight for a person of exactly 5 feet, plus a fixed increment for every inch above that. They differ only in the numbers, which came out of different research populations.
IBW = base weight + increment x (height in inches - 60)
where:
- base weight is the formula's value in kilograms at a height of 5 feet
- increment is the kilograms it adds for each inch above 5 feet
- height in inches - 60 is how far above 5 feet you are
| Formula | Men | Women | Notes |
|---|---|---|---|
| G. J. Hamwi (1964) | 48.0 kg + 2.7 kg per inch | 45.5 kg + 2.2 kg per inch | Written for medicinal dosage |
| B. J. Devine (1974) | 50.0 kg + 2.3 kg per inch | 45.5 kg + 2.3 kg per inch | The most widely used of the four |
| J. D. Robinson (1983) | 52.0 kg + 1.9 kg per inch | 49.0 kg + 1.7 kg per inch | Modification of Devine |
| D. R. Miller (1983) | 56.2 kg + 1.41 kg per inch | 53.1 kg + 1.36 kg per inch | Modification of Devine |
Take a man of 5 feet 10 inches, so 10 inches over the baseline. Devine gives 50 + (2.3 x 10), which is 73 kg or about 161 pounds. The same man gets 75 kg from Hamwi, 71 kg from Robinson and 70.3 kg from Miller. That is an 11 pound spread across four published formulas for one identical body, and it is the clearest evidence of how approximate any single figure is.
The formulas agree closely at 5 feet and fan apart as height increases, because Hamwi adds nearly twice as much per inch as Miller does. At 6 feet 4 inches the gap between them is wider still. Devine sits in the middle, which is part of why it became the default.
The healthy BMI range
The World Health Organization puts the healthy BMI band at 18.5 to 25 for adults of both sexes. Because BMI is weight divided by height squared, that band converts straight into a weight range for any given height.
Weight range = 18.5 x height² to 25 x height², with height in metres and weight in kilograms.
At 5 feet 10 inches, or 1.778 m, that is 58.5 kg to 79.0 kg, roughly 129 to 174 pounds. Notice it is a range rather than a point, which is the honest way to present this. Every IBW formula produces a single number, and every one of those numbers falls somewhere inside the healthy BMI band for the same height.
BMI is the metric clinicians reach for first, because it takes two measurements and predicts population-level risk of diabetes, heart disease and other conditions reasonably well. It fails on individuals for the same reason IBW does: it cannot tell muscle from fat. NICE guidance in the UK also applies lower cut-offs for people of South Asian, Chinese, Black African and African-Caribbean family background, where risk rises at a BMI of 23 rather than 25.
Children and teenagers
None of the above applies under 18. Children are still growing, and a weight that is right at 11 is wrong at 14, so their BMI has to be read against age and sex rather than against a fixed band. The Centers for Disease Control and Prevention publishes growth charts that do exactly that.
CDC BMI chart for boys between ages 2 and 20 (PDF)
CDC BMI chart for girls between ages 2 and 20 (PDF)
Read the charts by plotting age along the bottom and BMI up the side, then finding which percentile curve the point lands on. The CDC recommends children stay between the 5th and 85th percentile for their age. Below the 5th is underweight, 85th to 95th is overweight, and above the 95th is obese. A single reading matters far less than the direction of travel across several years, which is what the curves are drawn to show.
Where this calculator falls short
Every formula here was built to apply to as many people as possible, which means it fits nobody exactly. They take height and sex and nothing else. They do not account for physical disability, amputation, unusual body composition, activity level, or the ratio of muscle to fat that decides what a given weight actually means.
They also behave badly at the extremes. All four are anchored at 5 feet and extrapolate linearly from there, so someone well under 5 feet or well over 6 feet 6 inches is being served by a straight line drawn far past the data it was fitted to.
Use the output as a general guideline drawn from popular formulas. It is not a value you have to hit to be healthy.
Better questions than "what should I weigh?"
Waist circumference tells you more about metabolic risk than total weight does, because it measures where the fat is rather than how much of you there is. Fat around the organs behaves differently from fat on the hips and thighs.
Waist-to-height ratio is the simplest version: divide your waist by your height in the same units and aim to stay under 0.5. NICE adopted that threshold in 2022 precisely because it works across heights and body types where BMI struggles, and you need one tape measure to check it.
Body composition, if you can get it measured properly, answers the question all of these proxies are circling: how much of your weight is muscle and how much is fat. A DEXA scan is the reliable option. Bioimpedance scales are cheap and drift with hydration, though they track direction usefully over months.
Beyond that, the markers a clinician actually watches are blood pressure, resting heart rate, blood lipids, fasting glucose and how you sleep. All of them can improve substantially without the scale moving much at all.
Common questions
Frequently asked questions
It was created for drug dosing. Some medicines distribute through lean tissue rather than fat, so dosing a heavy patient on total weight overshoots. Devine published his formula in 1974 for gentamicin dosing, and Hamwi wrote his in 1964 for diabetic diet planning. Predicted body weight is still used to set ventilator tidal volumes at around 6 mL/kg in intensive care.
Devine is the most widely used and sits roughly in the middle of the four, but none is more correct than the others for predicting a healthy weight. For a 5 foot 10 inch man they give 70.3 kg, 71 kg, 73 kg and 75 kg, an 11 pound spread for the same body. Treat the range as the answer rather than any single figure.
No, not as a target. The formulas use only height and sex, so they cannot tell muscle from fat and were never designed as health goals. Fit athletes regularly come out overweight on IBW and BMI. Regular exercise, mostly unprocessed food and adequate sleep matter more than hitting a number from a 1974 dosing formula.
Wrap a tape around the smallest part of your wrist, just past the bone towards the hand, then compare it against your height. A woman over 5 feet 5 inches is small boned under 6.25 inches, medium from 6.25 to 6.5, and large above that. The wrist works because it carries almost no fat or muscle to distort the reading.
Take the WHO healthy BMI band of 18.5 to 25 and convert it for your height: weight equals BMI multiplied by height in metres squared. At 5 feet 10 inches that gives 58.5 kg to 79.0 kg, or about 129 to 174 pounds. Every IBW formula for that height falls inside this range.
Not directly in the formulas, which use only height and sex. Indirectly it does, because people lose height with age: about 1.5 inches for men and 2 inches for women by 70, and a shorter height gives a lower IBW. Muscle mass also declines while fat accumulates more easily, so the same weight represents a different body at 60 than at 25.
The CDC growth charts, which read BMI against age and sex rather than against a fixed band. The charts for boys and girls aged 2 to 20 are linked above. The CDC recommends staying between the 5th and 85th percentile for age, and the trend across several years matters far more than a single reading.
BMI is more useful because it gives a range rather than a single number and is what clinicians actually use to flag risk. Both share the same blind spot: neither can distinguish muscle from fat. Waist-to-height ratio is a good third check, and staying under 0.5 is the threshold NICE adopted in 2022.
Male bodies carry more muscle, which is denser than fat, along with higher bone density, and men are taller on average. Women carry a higher percentage of body fat while weighing less overall. Every one of the four formulas reflects this with a lower base weight for women, a smaller increment per inch, or both.
Yes. The formulas take height and sex and nothing else, so being above or below the figure says little on its own. Blood pressure, blood lipids, fasting glucose, fitness and sleep quality describe health far better, and all of them can improve substantially while the scale barely moves.