On a hospital ward in 1974, a pharmacist named B.J. Devine needed a fast way to dose gentamicin for a patient whose actual weight didn’t match his frame. There was no time for a research grant. Devine grabbed a decades-old rule of thumb, converted it to kilograms, and tucked it into a case study nobody expected to become famous. That quick fix is the Devine formula. It’s still the most cited ideal body weight equation in medicine, more than fifty years later. Here’s exactly how it works, where the numbers actually come from, and how it stacks up against the Hamwi, Robinson, and Miller equations you’ll see quoted everywhere else. Understanding the math behind it also explains why doctors still trust a shortcut that was never formally tested.
What Is the Devine Formula?
The Devine formula calculates ideal body weight (IBW) from height alone, using a separate constant for men and women. It’s a straight line: a fixed starting weight at 5 feet, plus a fixed amount for every inch above that.
Men: IBW = 50 kg + 2.3 kg × (height in inches − 60) Women: IBW = 45.5 kg + 2.3 kg × (height in inches − 60)
Both sexes add the same 2.3 kg per inch. Only the base weight at 5 feet changes — 50 kg for men, 45.5 kg for women.
Worked example — 5’11” man (71 inches): IBW = 50 + 2.3 × (71 − 60) = 50 + 25.3 = 75.3 kg (166.1 lb)
Worked example — 5’3″ woman (63 inches): IBW = 45.5 + 2.3 × (63 − 60) = 45.5 + 6.9 = 52.4 kg (115.5 lb)
Notice what’s missing from that equation. No age, no wrist size, no weight history. Just two numbers and a ruler. That simplicity is exactly why the Devine formula spread through hospitals so fast. It’s also, as you’ll see below, exactly why it draws criticism today.
Graph it and you get a straight line, not a curve. Every additional inch adds precisely 2.3 kg, whether you’re going from 5’0″ to 5’1″ or from 6’5″ to 6’6″. Real human weight doesn’t scale that evenly — bone structure and typical build shift in more complicated ways across a height range — but a straight line is trivial to compute by hand, and in 1974 that mattered more than statistical elegance. It also behaves oddly at the edges: push it much below 5 feet and the “minus 60” term turns negative, dragging the result down in a way nobody designing a serious growth model would allow. The formula was built for an average adult inpatient, not an edge case.
Where the Devine Formula Actually Came From
Most people assume a formula this widely used was built from a large clinical trial. It wasn’t. The real story is stranger, and it explains a lot about why the Devine formula looks the way it does.
A Rule of Thumb Borrowed From an Army Doctor
The lineage starts with Pierre Paul Broca, a French army surgeon who in 1871 proposed one of the first height-based weight estimates: roughly, height in centimeters minus 100 equals weight in kilograms. Over the following decades, someone (the record doesn’t say who) adapted Broca’s idea into an English-language shortcut still taught in nursing schools: 100 pounds for the first 5 feet in women, 110 pounds for men, plus 5 pounds for every inch after that. It was never a study. It was a mnemonic, passed down by word of mouth between practitioners who needed a fast estimate at the bedside.
One Pharmacy Case Study, Fifty Years of Use
B.J. Devine didn’t invent new math. He converted that old pounds-and-inches rule of thumb into kilograms and metric height, then published it inside a single case report, “Gentamicin Therapy,” in Drug Intelligence and Clinical Pharmacy, 1974 (Devine BJ, DICP 1974;8:650–655). By his own account, the numbers reflected empiric estimates from his mentor, Dr. Margaret McCarron, not a dedicated research population. A pharmacy education paper later traced this full lineage in detail (Pai & Paloucek, The Origin of the “Ideal” Body Weight Equations), and its conclusion is blunt: the Devine formula was never formally validated against an actual weight dataset. It got adopted anyway, because it worked well enough for dosing decisions and because nothing simpler came along to replace it. Fifty years of institutional habit did the rest.
Devine Formula vs. Hamwi, Robinson, and Miller
Three other equations get quoted alongside the Devine formula constantly, and they’re close cousins rather than competitors built from scratch. Each nudges the base weight or the per-inch constant in a slightly different direction.
| Formula | Men (per inch over 5 ft) | Women (per inch over 5 ft) | Origin |
|---|---|---|---|
| Devine (1974) | 50 kg + 2.3 kg | 45.5 kg + 2.3 kg | Gentamicin dosing case study |
| Hamwi (1964) | 48 kg + 2.7 kg | 45.4 kg + 2.2 kg | Diabetic dietary counseling |
| Robinson (1983) | 52 kg + 1.9 kg | 49 kg + 1.7 kg | Refinement of Devine, lower estimates |
| Miller (1983) | 56.2 kg + 1.41 kg | 53.1 kg + 1.36 kg | Metropolitan Life actuarial tables |
Run all four against a 5’11” man and the spread becomes obvious: 75.3 kg (Devine), 77.7 kg (Hamwi), 72.9 kg (Robinson), and 71.7 kg (Miller). That’s a 6 kg gap between the highest and lowest estimate for one identical height. None of these numbers is a precise personal target, and treating any single one that way misses the point of running all four.
The Hamwi formula predates Devine’s by a decade. Ernest Hamwi built the Hamwi equation for diabetic patients who needed a quick nutritional counseling target, not a drug-dosing reference, and the Hamwi method uses a steeper per-inch increment for men (2.7 kg vs. Devine’s 2.3 kg). That’s why the Hamwi formula tends to run higher than Devine at taller heights. The Robinson formula arrived in 1983 as a deliberate correction, since its authors thought Devine’s numbers ran slightly high and proposed a gentler slope. The Miller formula, published the same year, drew on Metropolitan Life Insurance actuarial tables rather than clinical dosing needs, which is why it produces the flattest curve of the four and diverges the most from the Devine formula at greater heights.
None of these four is “more correct” in an absolute sense. They’re four independent guesses at the same target, built for four different purposes, and Devine’s version simply became the one medicine settled on. Pharmacy departments occasionally standardize on Robinson instead for pharmacokinetic calculations, arguing its lower estimates reduce overdosing risk in lean patients — but the majority default remains the original 1974 equation, mostly out of institutional habit rather than evidence that it outperforms the alternatives.
Where the Devine Formula Is Actually Used Today
Given its shaky statistical origin, you might expect the Devine formula to have been quietly retired. The opposite happened. It’s arguably more embedded in modern clinical practice now than it was in 1974.
Drug dosing. Aminoglycoside antibiotics (gentamicin, tobramycin), vancomycin, and several chemotherapy agents are dosed against ideal body weight rather than actual weight, because dosing obese or underweight patients by scale weight alone risks toxicity or underdosing. The Devine formula remains the default reference in most hospital pharmacy protocols for this exact calculation.
Adjusted body weight (AdjBW). When a patient’s actual weight sits more than 30% above their Devine-formula IBW, pharmacists apply: AdjBW = IBW + 0.4 × (actual weight − IBW). This split-the-difference figure shows up constantly in vancomycin dosing for patients with obesity.
Ventilator settings. This is the use case most people never hear about. Lung-protective ventilation protocols (the ones that came out of the landmark ARDSNet trial) set tidal volume at roughly 6 mL per kilogram of “predicted body weight.” Predicted body weight is calculated with the Devine formula (standardization research on this exact calculation). Get the height wrong, or use actual weight instead of predicted weight in an obese patient, and the tidal volume setting can drift outside the protective range. A formula built for a single antibiotic case study in 1974 now quietly shapes ICU ventilator settings worldwide.
Nutrition support. Registered dietitians calculating caloric and protein targets for critically ill or obese patients often anchor on ideal body weight rather than actual weight, since basing energy needs on actual weight in a heavier patient can substantially overshoot true requirements. A patient in the ICU on tube feeding may have their goal calories calculated as roughly 22–25 kcal per kilogram of IBW rather than actual body weight — another quiet, everyday application of a formula most patients never hear named.
If you want to see your own number rather than just the theory, our breakdown of healthy weight ranges by height walks through how these same formulas apply to an individual result, and pairs well with a BMI calculator or body fat calculator if you want the fuller picture beyond height and sex alone.
Frequently Asked Questions
Who actually created the Devine formula, and why?
Pharmacist B.J. Devine published it in 1974 inside a single gentamicin dosing case report, crediting the underlying numbers to his mentor Dr. Margaret McCarron’s clinical estimates. It wasn’t built from a dedicated research study — it was a practical shortcut for antibiotic dosing that happened to stick.
Is the Devine formula still used in hospitals today?
Yes, extensively. It remains the standard reference for dosing several antibiotics and chemotherapy drugs by ideal body weight, and it’s the formula behind “predicted body weight” in lung-protective ventilator protocols used in most ICUs.
How different are the Devine formula and the Robinson formula in real numbers?
At 5’11”, Devine returns 75.3 kg and Robinson returns 72.9 kg — a gap of about 2.4 kg. The gap widens at taller heights because Robinson’s per-inch constant (1.9 kg) is smaller than Devine’s (2.3 kg).
Does the Devine formula work for people under 5 feet tall?
Not reliably. Below 60 inches, the height-minus-60 term goes negative, which can push the result down in ways the original formula was never designed to handle. Most clinical references limit Devine formula use to adults at or above 5 feet.
Why does the Devine formula use the same 2.3 kg per inch for men and women?
Nobody knows for certain — Devine never published a rationale beyond the base weights he adapted from the pounds-based rule of thumb. Later formulas like Hamwi and Miller each chose different per-inch constants for men and women, suggesting later authors weren’t convinced Devine’s shared slope was correct either.
Is the Devine formula the same thing as “predicted body weight” (PBW)?
Functionally, yes. In ventilator and critical care literature, predicted body weight is calculated using the exact same Devine formula equation — the name changes depending on the clinical context, but the math underneath is identical.
Was the Devine formula ever formally validated?
No. Pharmacy history research has confirmed it was published as an empiric estimate, not tested against a measured weight dataset. It persisted through institutional adoption and repeated citation rather than clinical trial evidence.
What came before the Devine formula?
An informal pounds-and-inches rule of thumb, itself derived from Pierre Paul Broca’s 1871 height-based weight estimate. Devine’s contribution was converting that folk rule into metric units for a specific dosing case, not inventing a new method from scratch.
Does the Devine formula account for muscle mass or body frame?
No. It’s a two-variable equation — height and sex, nothing else. A powerlifter and a sedentary office worker of identical height get the identical IBW figure, even though their healthy weights in reality could differ by 20 kg or more. That blind spot is precisely why it’s a dosing reference and not a fitness goal.
Why hasn’t a better formula replaced the Devine formula by now?
Partly inertia, partly practicality. Newer, more sophisticated body composition tools exist — bioelectrical impedance, DEXA scans, skinfold calipers — but none of them fit into a two-second bedside calculation the way Devine’s equation does. In a busy pharmacy or ICU, a formula you can compute on a napkin still beats a more accurate method that tak
The Devine Formula, in Perspective
The Devine formula isn’t a law of biology. It’s a fifty-year-old pharmacy shortcut that outlived its original case study by decades, mostly because nothing simpler ever replaced it. Treat the number it gives you as a clinical reference point for dosing and ventilator math, not a personal verdict on how much you should weigh. Knowing where it came from, an army doctor’s rule of thumb filtered through one gentamicin case report, makes the number a lot easier to put in its proper place. If you’re curious where you land against it and the other three formulas, run your own height through the calculators linked above and compare the spread for yourself.