Article — Ideal Weight Calculator
Ideal Weight Calculator — Robinson, Miller, Devine, and Hamwi
Ideal body weight (IBW) is a single estimated weight target derived from height and sex, used in clinical medicine for drug dosing, mechanical ventilation, and nutrition planning. Four standard formulas exist: Devine (1974), Robinson (1983), Miller (1983), and Hamwi (1964). At 175 cm a male IBW is roughly 70 kg; at the same height a female IBW is about 65 kg. The four formulas typically span 4 to 8 kg at adult heights.
IBW is not a fitness goal. It is a clinical anchor, designed to standardize dose calculations and ventilator settings across body types. Real health depends on body composition, frame, ethnicity, and age — none of which the four classic formulas account for. The calculator above shows all four values plus the WHO healthy BMI range, so you can compare a single target value against a clinical band.
What is ideal weight?
Ideal weight is a clinical concept that originated in life-insurance actuarial tables in the early 20th century. Metropolitan Life Insurance published height-weight tables in 1942 and 1959, based on millions of policyholders, that linked weight ranges to mortality outcomes. Those tables seeded the four formulas now in clinical use.
The formulas share a structure. Each takes a base weight at 5 feet (60 inches) of height and adds a per-inch coefficient for every inch above 60. Sex sets both the base and (in three of the four) the slope. The output is a single weight in kilograms — the "ideal" value for that height and sex.
Devine's 1974 formula was originally created to dose aminoglycoside antibiotics, not to set fitness targets. The drug distributes mostly to lean tissue, so using actual body weight in obese patients overdoses them. The "ideal" weight in the formula's name refers to ideal pharmacokinetic distribution, not ideal appearance or health.
The four ideal weight formulas
All four formulas use inches above 60 (5 feet) as the input variable. The differences are in the constants:
Devine M: 50.0 + 2.3 × (h−60) Devine F: 45.5 + 2.3 × (h−60)Robinson M: 52.0 + 1.9 × (h−60) Robinson F: 49.0 + 1.7 × (h−60)Miller M: 56.2 + 1.41 × (h−60) Miller F: 53.1 + 1.36 × (h−60)Hamwi M: 48.0 + 2.7 × (h−60) Hamwi F: 45.5 + 2.2 × (h−60)Hamwi came first, designed for bedside mental math (originally 106 lb at 5 ft + 6 lb per inch for men). Devine adapted it for kilograms and tightened the slope for antibiotic dosing. Robinson and Miller both updated the data using Metropolitan Life's 1979 tables.
Ideal weight versus BMI
Ideal weight gives a single value. BMI gives a range. The WHO healthy BMI band (18.5 to 24.9) at 175 cm spans roughly 56.6 to 76.2 kg, while the average IBW for a 175 cm male is about 70 kg — comfortably inside the BMI range.
The two metrics serve different purposes. BMI is a population screening tool — useful for tracking obesity rates and assessing cardiovascular risk across groups. IBW is a clinical calculation tool — useful for medication dosing and ventilator tidal volume. Neither captures body composition. A muscular athlete and a sedentary office worker can share a BMI of 26 yet have wildly different metabolic profiles.
How to pick an ideal weight formula
For US clinical pharmacology, Devine is the default. It is built into most electronic medical record systems and dosing references. For nutrition planning, Hamwi is widely used because it was designed for that purpose. Robinson and Miller are common in research papers. The four often differ by less than a kilogram at heights between 165 and 180 cm; outside that range the spread grows.
- Devine 1974 — US clinical pharmacology default, antibiotic dosing
- Robinson 1983 — Updated Metropolitan Life data, research literature
- Miller 1983 — Higher base, lower slope, less common
- Hamwi 1964 — Easy mental math, dietetics
- Average — A reasonable consensus value
- WHO healthy BMI — Range, not single target (18.5-24.9)
Where ideal weight is used in clinical practice
Five settings dominate. First, drug dosing for medications that distribute mostly to lean tissue — aminoglycosides, vancomycin, heparin, some chemotherapy. Using actual weight in obese patients can overdose them; using IBW or an adjusted body weight gives safer plasma levels. Second, ventilator tidal volume in critical care; lung size scales with height, so 6 mL/kg of IBW is the ARDSnet protocol.
Renal replacement therapy uses IBW-scaled body water for dialysis dose and ultrafiltration. Enteral and parenteral nutrition planning often reference IBW for protein and calorie targets in obese patients. Obstetric care uses pre-pregnancy IBW as the anchor for gestational weight gain.
The formulas were derived from sedentary insurance populations, not athletes. A muscular 180 cm man at 90 kg with 10% body fat is well above the 75 kg IBW value but typically in excellent health. Use body composition measurements (DXA, BIA) and metabolic markers (lipids, glucose) to evaluate actual health, not IBW.
Limitations of ideal weight formulas
The four formulas were derived from US adults in the mid-20th century, mostly white, with a relatively narrow height range. Modern critique focuses on three gaps. First, applicability outside that source population. Asian and Latin American populations have different body composition at any given height; some Asian-specific BMI cutoffs use 23 (not 25) as the overweight threshold for this reason.
Second, the formulas extrapolate poorly outside 60 to 76 inches (152 to 193 cm). At 200 cm the predicted IBW values diverge by 10+ kg between formulas. Third, no formula accounts for age. Older adults lose lean mass (sarcopenia) — predicted IBW remains constant, but actual healthy weight may drop with age in real bodies.
For pediatric or elderly patients, do not use the adult IBW formulas. Pediatric medicine uses growth charts (CDC or WHO) instead. Geriatric medicine increasingly uses sarcopenia-adjusted targets that allow lower lean mass.
A brief history of ideal weight tables
Metropolitan Life published the first widely used height-weight tables in 1942, drawn from policyholder mortality data, with revisions in 1959 and 1983. The "ideal" in ideal weight comes from the mortality minimum in those tables, not aesthetic judgment.
Hamwi simplified them into a one-line formula in 1964. Devine adapted it in 1974 for antibiotic pharmacokinetics. Robinson and Miller revisited the data in 1983. Since then no major new IBW formula has displaced the four classics.
Ideal weight and real-world health
Treat ideal weight as one data point among many. It is useful for clinical dosing, ventilator settings, and as a rough reference target. It is not useful as a fitness goal, particularly for athletes, older adults, or people outside the source populations. The WHO BMI range gives a wider, more inclusive band; body composition measurements give the actual answer.
The most actionable comparison is IBW versus actual weight, not IBW versus the perfect number. If actual weight sits 20% above IBW and BMI is in the obese range, the gap is clinically meaningful. If actual weight sits 5% above and body composition is healthy, the gap is statistical noise.