Ideal Body Weight Calculator
Compare estimates from 4 clinical formulas — Devine, Robinson, Miller, and Hamwi
Your Ideal Body Weight Estimates
These formulas were developed for clinical reference (drug dosing, ventilator settings). They do not account for muscle mass, ethnicity, or body composition. Consult a healthcare professional for personalised guidance.
Devine vs Robinson vs Miller vs Hamwi: Which Ideal Body Weight Formula Should You Actually Trust?
Walk into any hospital pharmacy or ICU and you will hear the phrase "ideal body weight" tossed around casually — as if a single, agreed-upon number exists for every person on the planet. In reality, four separate formulas have competed for clinical dominance for more than sixty years, each producing a slightly different answer, and each carrying its own historical baggage. Understanding what separates them matters whether you are a clinician calculating drug doses, a dietitian setting calorie targets, or simply someone trying to make sense of a number on a health chart.
Why Ideal Body Weight Exists — and What It Was Never Meant to Do
The concept of ideal body weight (IBW) was not born in a gym or a diet book. It came out of insurance actuarial tables in the 1940s and 1950s, when the Metropolitan Life Insurance Company correlated body weight with mortality data across policyholders. The goal was purely statistical: find the weight associated with the longest survival at a given height. From that unglamorous origin, clinicians borrowed the concept for practical purposes — calculating drug doses (especially for medications with narrow therapeutic windows), estimating tidal volumes for mechanical ventilation, and setting nutritional targets in hospital settings.
This context is crucial because it explains something that surprises most people: IBW formulas were calibrated for clinical utility, not for telling individuals what they should weigh to be healthy. They do not account for muscle mass, ethnicity, age beyond adulthood, or body composition. A heavily muscled athlete and a sedentary person of the same height and sex will get identical IBW estimates from all four formulas. Keep that in mind throughout this comparison.
The Hamwi Formula (1964): The Rule-of-Thumb Pioneer
Dr. G.J. Hamwi introduced his formula in 1964 primarily for use in diabetes nutrition counseling. It is the most hands-on of the four — designed to be calculated quickly without a pocket calculator. The base is 48 kg for men and 45.4 kg for women at exactly 5 feet, adding 2.7 kg per inch for men and 2.2 kg per inch for women above that baseline.
Because it uses the largest per-inch increment for men among the four formulas, Hamwi consistently produces the highest IBW estimates for taller males. At 5'10", for instance, Hamwi estimates roughly 75.4 kg for a man — noticeably heavier than what Robinson or Devine suggest. For dietitians, this higher figure sometimes translates into more generous calorie prescriptions, which can be appropriate for physically active patients. The downside is that the formula can slightly overestimate IBW for shorter individuals.
The Devine Formula (1974): The Clinical Workhorse
Dr. B.J. Devine published his formula in 1974 in a drug dosing paper — its original purpose was calculating gentamicin doses, not body composition science. The base values are 50 kg for men and 45.5 kg for women at 5 feet, adding 2.3 kg per inch for both sexes above that height.
Despite its narrow origins, Devine became the most widely cited IBW formula in medicine. It appears in ventilator protocols, anesthesia guidelines, and pharmacokinetic references worldwide. That prevalence is somewhat ironic: the formula itself was never validated against a robust dataset — Devine essentially back-calculated it from clinical intuition. Nevertheless, its ubiquity means that if you see "IBW" cited in a medical chart without further specification, Devine is almost certainly what was used. It tends to produce moderate estimates, sitting between the higher Hamwi values and the lower Robinson estimates for most heights.
The Robinson Formula (1983): The Conservative Counterpoint
J.D. Robinson and colleagues published their formula in 1983, explicitly as a refinement of Devine. The base is 52 kg for men and 49 kg for women at 5 feet, but the per-inch increment drops to just 1.9 kg for men and 1.7 kg for women — the smallest increments among the four formulas.
The practical result is striking: Robinson agrees reasonably well with Devine at moderate heights (around 5'5" to 5'8"), but diverges noticeably as height increases. A 6-foot man gets approximately 70.8 kg from Robinson versus 73.5 kg from Devine — a difference of nearly 2.7 kg. For very tall individuals, Robinson consistently produces the lowest IBW estimates of the four formulas. Some pharmacists prefer Robinson precisely because it is more conservative, which can reduce the risk of overdosing medications in tall patients. Critics argue it underestimates appropriate weight for taller, naturally larger-framed people.
The Miller Formula (1983): The Middle-Ground Option
Published in the same year as Robinson, the Miller formula takes yet another approach. The base is 56.2 kg for men and 53.1 kg for women at 5 feet — the highest base of all four formulas — but the per-inch increment is the gentlest: 1.41 kg for men and 1.36 kg for women.
This unusual combination means Miller produces the highest IBW estimates for very short individuals but slopes upward more gradually than the others. For a 5'2" woman, Miller returns a notably higher estimate than Hamwi or Devine, which can feel more realistic for petite but solidly built frames. For taller individuals, Miller's estimates fall in the middle of the pack. Some researchers have suggested Miller is more appropriate for certain clinical populations where the other formulas systematically over- or under-estimate lean mass, though it has never achieved the mainstream adoption of Devine.
Frame Size: The Adjustment No Formula Originally Included
None of the four original formulas incorporated body frame size — they assumed a "medium" frame by default. The standard clinical practice of adjusting by ±10% for small or large frames came later, borrowed from the Metropolitan Life tables. Frame size is typically estimated by wrist circumference or elbow breadth measurement rather than self-report, so the adjustment is somewhat subjective when done informally.
What is interesting is how frame adjustment interacts with each formula differently. Because Hamwi already produces higher base estimates, a large-frame Hamwi value for a tall man can exceed 80 kg — plausibly realistic for a broad-shouldered individual, but potentially misleading for someone of average build who simply guesses "large." The frame size option in this calculator is best used when you have an objective measurement to support your choice.
Side-by-Side: Where the Formulas Agree and Diverge
The formulas converge most tightly around heights of 5'5" to 5'7" for women and 5'7" to 5'9" for men — the range the original datasets were probably most populated with. As you move toward the extremes of the height spectrum, the estimates spread apart significantly. For a 5-foot woman, the four formulas range from 45.4 kg (Hamwi) to 53.1 kg (Miller) — a spread of nearly 8 kg, which is substantial. For a 6'2" man, the spread is somewhat smaller in absolute terms but still spans roughly 5 kg between Robinson and Hamwi.
This divergence is not a flaw to be fixed — it reflects genuine scientific uncertainty about what "ideal" means across the full height range. Rather than agonizing over which formula is correct, most clinicians use all available estimates as a range and apply clinical judgment to determine where within that range a particular patient's target should fall.
What These Numbers Should — and Should Not — Mean to You
If you are outside a clinical context, treat IBW estimates as one rough data point among many. They say nothing about metabolic health, cardiovascular fitness, bone density, or muscle-to-fat ratio. A person 10 kg above their Devine IBW with a high muscle mass and excellent blood markers is almost certainly healthier than someone at their exact IBW with a sedentary lifestyle and poor metabolic numbers.
Where IBW calculations genuinely earn their keep is in situations requiring a standardized, height-based estimate independent of actual weight: calculating appropriate antibiotic doses in obese patients, setting initial tidal volume targets in mechanically ventilated patients, or establishing baseline nutritional needs when actual body weight would distort the calculation. For those purposes, knowing which formula a protocol specifies — and using the same one consistently — matters more than debating which is most accurate.
Use the four estimates from this calculator as a compass, not a verdict. They tell you the general territory your body weight should be in for your height and sex. Whether you land at the Devine number, the Robinson number, or somewhere else in that range is a conversation worth having with a healthcare provider who knows your full clinical picture.