What is ideal body weight and how is it calculated?

Ideal body weight (IBW) is the weight that corresponds to a healthy body composition for a given height and frame size. There are four common formulas: Devine (1974, drug-dosing standard), Robinson (1983, Metropolitan Life Insurance based), Miller (1983, HANES based), and BMI-based (22 kg/m² midpoint). The Devine formula is: Men: IBW = 50 + 2.3 × (inches above 5 feet); Women: IBW = 45.5 + 2.3 × (inches above 5 feet). For a 6'0" man: IBW = 77.6 kg. For a 5'6" woman: IBW = 59.3 kg. The BMI-based formula is: IBW = 22 × height (m²), giving 73.9 kg for a 183 cm adult.

Why is the Devine 1974 formula still used?

The Devine 1974 ideal body weight formula is still the standard for drug dosing in clinical pharmacology 50 years after publication. The original paper was on gentamicin dosing in obese patients, where total-body-weight dosing causes supratherapeutic drug levels because the drug distributes poorly in fat tissue. The Devine formula provides a quick reference weight that approximates lean body mass for dosing purposes. It has been validated for use with acetaminophen, anesthetic drugs, contrast agents, and aminoglycosides. The formula is also taught in USMLE pharmacology courses because it provides consistent values across patient populations and is simple to calculate at the bedside.

What is the difference between Devine, Robinson, and Miller formulas?

The three ideal weight formulas (Devine 1974, Robinson 1983, Miller 1983) all use linear scaling with height above 5 feet but differ in intercept and slope: Devine: Men 50 kg + 2.3 kg/in; Robinson: Men 52 kg + 1.9 kg/in; Miller: Men 56.2 kg + 1.41 kg/in. The differences reflect different reference datasets (Devine used a UK clinical reference; Robinson used Metropolitan Life 1959; Miller used HANES). For most adults, the formulas agree within 4 kg. The choice of formula is conventional; the variation between formulas for a given height is smaller than the variation across individuals of that height due to frame size, body composition, and ethnicity.

What does BMI 22 mean for ideal weight calculation?

BMI 22 is the statistical midpoint of the WHO healthy BMI range (18.5–24.9), associated with the lowest all-cause mortality in modern cohorts. The Global BMI Mortality Collaboration 2016 meta-analysis (10.6 million subjects) found lowest mortality at BMI 20–25 kg/m² with the nadir at 22–23. Using BMI 22 as the "ideal": ideal weight = 22 × height (m²). For a 175 cm adult: 67.4 kg; for a 165 cm adult: 59.9 kg; for a 200 cm adult: 88.0 kg. The BMI-based formula captures statistical population-level health, while the older Devine/Robinson/Miller formulas reflect historical insurance-table weights.

How does frame size affect ideal weight?

Frame size adjustments for ideal weight can produce 20% variation even at the same height. The Devine formula includes a frame adjustment: small frame −10%, large frame +10%. Frame is measured by wrist circumference (small 7.5" men, >6.5" women), elbow breadth, or body composition. For a 175 cm man, the ideal weight range across frame sizes spans 60–75 kg — larger than the variation across formulas (~4 kg). Modern clinical practice often recommends aiming for any weight within the WHO healthy BMI range (18.5–24.9) with frame adjustments, rather than a single specific ideal value.

Why is ideal body weight important for drug dosing?

Ideal body weight is clinically important for drugs that distribute primarily in lean body mass rather than fat tissue. Aminoglycoside antibiotics (gentamicin, tobramycin) have been dosed by IBW since 1974 to avoid nephrotoxicity in obese patients. Other drugs dosed by IBW include acetaminophen (FDA advisory 2011), several anesthetic agents (propofol, thiopental, rocuronium), and contrast dyes used in radiology. The Devine 1974 IBW formula was originally derived for gentamicin and has remained the clinical standard for 50 years. Recent literature 2018–2024 recommends "adjusted body weight" (ABW = IBW + 0.4 × (actual − IBW)) for moderate-to-morbid obesity for more accurate dosing.

What is a healthy BMI range vs ideal weight?

The WHO healthy BMI range of 18.5–24.9 is more flexible than a single ideal weight value because it accommodates frame size, muscle mass, and ethnicity differences. For a 175 cm adult, the healthy range is 56.7–76.3 kg. The "ideal" in this range can vary: a large-framed 175 cm man might appropriately weigh 76 kg (BMI 24.8), while a small-framed 175 cm woman might appropriately weigh 60 kg (BMI 19.6) — both are within the healthy range. Modern clinical nutrition and weight management commonly use the healthy BMI range rather than a single "ideal weight" target. The target of BMI 21–23 is supported by contemporary mortality data as the lowest-risk subset. relatedtopics: - 'bmi-calculator' - 'body-fat-calculator' - 'bmr-calculator' - 'weight-loss-calculator' - 'calorie-deficit-calculator' - 'frame-size-calculator' ---

Ideal Weight: The 1974 Drug-Dosing Formula That Became a 50-Year Fitness Standard

In 1974, Benjamin Devine at the University of Auckland published a paper in Metabolism titled "Gentamicin Therapy" that included a simple ideal body weight formula: Men: 50 kg + 2.3 kg per inch above 5 feet; Women: 45.5 kg + 2.3 kg per inch above 5 feet. The reference point was a 5'7" (170 cm) male weighing 70 kg — the "standard" human used in pharmacology teaching. He needed an exact weight for drug dosing because gentamicin distributes poorly in fat tissue, so overweight patients given a dose calculated by total body weight would be overdosed. The formula was meant to be a clinical approximation tool, but it became so widely cited that 50 years later, USMLE Step 1 students still memorise it for drug-dosing questions.

Devine 1974 — the formula that survived 50 years
Robinson 1983 and Miller 1983 — the modifications
BMI-based — the 22 kg/m² midpoint
Frame size — the often-overlooked variable
Healthy BMI range vs ideal weight target
Drug-dosing applications — where ideal weight matters clinically
Frequently Asked Questions

Devine 1974 — the formula that survived 50 years

The Devine 1974 ideal body weight formula is the most cited equation in clinical pharmacology:

Devine 1974 Formulas

Men: IBW (kg) = 50 + 2.3 × (height in inches above 5 feet)

Women: IBW (kg) = 45.5 + 2.3 × (height in inches above 5 feet)

The formulas were derived from a population reference and validated against introspection — Devine proposed the linear formula as a reasonable approximation to the Metropolitan Life Insurance 1959 height-weight tables, which were the standard reference for healthy weight at the time. The frame-of-reference is that a "ideal" 5'0" man weighs 50 kg (110 lb) and a "ideal" 5'0" woman weighs 45.5 kg (100 lb), with each additional inch adding 2.3 kg (~5 lb) to both male and female IBW.

For a 6'0" (183 cm) man, IBW = 50 + 2.3 × (72 − 60) = 50 + 2.3 × 12 = 50 + 27.6 = 77.6 kg. For a 5'6" (168 cm) woman, IBW = 45.5 + 2.3 × (66 − 60) = 45.5 + 13.8 = 59.3 kg. The linear scaling with height reflects the assumption that lean mass scales approximately with height, and the reference individual (170 cm/70 kg male) is taken as the "average healthy adult."

Devine 1974 Sample Computations by Height

Height (imperial)	Height (cm)	Men IBW (kg)	Men IBW (lb)	Women IBW (kg)	Women IBW (lb)
5'0"	152	50.0	110.2	45.5	100.3
5'2"	157	54.6	120.4	50.1	110.5
5'4"	163	59.2	130.5	54.7	120.6
5'6"	168	63.8	140.6	59.3	130.7
5'8"	173	68.4	150.8	63.9	140.9
5'10"	178	73.0	160.9	68.5	151.0
6'0"	183	77.6	171.1	73.1	161.2
6'2"	188	82.2	181.2	77.7	171.3
6'4"	193	86.8	191.4	82.3	181.4

Source: Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650-655. Formulas are linear extrapolation from the 170 cm / 70 kg male and 170 cm / 65 kg female references.

Robinson 1983 and Miller 1983 — the modifications

The Robinson and Miller formulas were published in 1983 as alternative ideal body weight formulas, both building on the Devine 1974 concept but using different reference weights.

Robinson 1983 Formulas

Men: IBW (kg) = 52 + 1.9 × (height in inches above 5 feet)

Women: IBW (kg) = 49 + 1.7 × (height in inches above 5 feet)

Robinson used Metropolitan Life Insurance 1959 build standards as the reference. The slope (1.9 kg/inch for men) is shallower than Devine (2.3 kg/inch) because Robinson's reference individual (5'7" man weighing 71 kg) is somewhat heavier relative to height than Devine's. For a 6'0" man: IBW = 52 + 1.9 × 12 = 74.8 kg (vs Devine 77.6 kg).

Miller 1983 Formulas

Men: IBW (kg) = 56.2 + 1.41 × (height in inches above 5 feet)

Women: IBW (kg) = 53.1 + 1.36 × (height in inches above 5 feet)

Miller used the US Health and Nutrition Examination Survey (HANES) reference weights. The slope (1.41 kg/inch) is even shallower, indicating a smaller weight gain per inch of height. For a 6'0" man: IBW = 56.2 + 1.41 × 12 = 73.1 kg.

The three formulas (Devine, Robinson, Miller) differ in intercept and slope, producing a range of 4–6 kg for any adult height. The choice of formula is conventional — most USMLE-Pharmacology sources use Devine; most clinical nutritionists use BMI-based; the variation between formulas for a given adult is smaller than the variation across individuals of the same height with different frame sizes, body composition, and ethnic background.

Comparison of Devine, Robinson, Miller for a 6'0" (183 cm) Male

Formula	Reference (kg)	Per-inch Slope (kg/in)	6'0" IBW (kg)	Difference vs Devine
Devine 1974	50 (5'0" male)	2.3	77.6	Reference
Robinson 1983	52 (5'0" male)	1.9	74.8	-2.8 kg
Miller 1983	56.2 (5'0" male)	1.41	73.1	-4.5 kg
BMI 22 mid-point	n/a (height² dependent)	n/a	73.9	-3.7 kg

BMI-based — the 22 kg/m² midpoint

A fourth approach, increasingly preferred in modern clinical practice, defines "ideal weight" as the weight corresponding to a BMI of 22 kg/m² — the midpoint of the WHO healthy BMI range (18.5–24.9). The formula is:

BMI-Based Ideal Weight: IBW (kg) = 22 × height (m)²

For a 175 cm adult: IBW = 22 × (1.75)² = 22 × 3.0625 = 67.4 kg. For a 165 cm adult: IBW = 22 × (1.65)² = 22 × 2.7225 = 59.9 kg. For a 200 cm very tall adult: IBW = 22 × (2.00)² = 88.0 kg.

The 22 kg/m² figure is supported by the Global BMI Mortality Collaboration's 2016 meta-analysis (10.6 million subjects, The Lancet), which found that in never-smokers without pre-existing disease, all-cause mortality was lowest at BMI 20–25 kg/m² with the nadir at approximately 22–23 kg/m². For populations where the lowest mortality is in the upper half of the healthy range, the BMI-based formula may be better than older ideal-weight formulas derived from insurance tables.

BMI-Based Ideal Weight Across Heights

Height (cm)	BMI 18.5 (kg)	BMI 22 (kg)	BMI 24.9 (kg)	WHO Healthy Range
152 (5'0")	42.7	50.8	57.5	42.7–57.5
163 (5'4")	49.2	58.5	66.2	49.2–66.2
175 (5'9")	56.7	67.4	76.3	56.7–76.3
183 (6'0")	62.0	73.7	83.4	62.0–83.4
193 (6'4")	69.0	82.0	92.8	69.0–92.8

Frame size — the often-overlooked variable

Frame size is a major determinant of ideal weight variation even at the same height. The Devine formula includes an explicit frame adjustment:

Small frame: IBW − 10% of base
Medium frame: IBW (base formula)
Large frame: IBW + 10% of base

Frame is measured by:

Wrist circumference (simplest method, validated against bone measurements)
- Small: <6.5" men (16.5 cm), <5.5" women (14.0 cm)
- Medium: 6.5"–7.5" men, 5.5"–6.5" women
- Large: >7.5" men (19 cm), >6.5" women (16.5 cm)
Elbow breadth (skeletal frame width, more accurate but requires measurement)
Body composition assessment (DXA scan; not practical for routine)

For a 175 cm man with large frame vs small frame, the ideal weight range differs by 20%: 67.4 × 1.10 = 74.1 kg (large frame) vs 67.4 × 0.90 = 60.7 kg (small frame). This range exceeds the formula-to-formula variation (~4 kg) and is the dominant source of "ideal weight" disagreement across individuals.

Healthy BMI range vs ideal weight target

For practical weight management, the WHO healthy BMI range (18.5–24.9) is more useful than a single ideal weight. The range accommodates frame size differences automatically and reduces the temptation to chase a specific number. For most adults, weight management targets should fall within the range:

Lower limit: BMI 18.5 — below this, hormonal disruption is common
Upper limit: BMI 24.9 — above this, cardiometabolic risk begins to increase
Optimal target: BMI 21–23 — lowest all-cause mortality in modern cohorts

For specific populations:

Asian populations: target BMI 18.5–22.9 (WHO 2004 Asian BMI cutoffs)
Older adults (≥65): target BMI 23–27 (obesity paradox, optimal survival at higher BMI)
Athletes with high muscle mass: use body composition (% body fat) rather than BMI

Drug-dosing applications — where ideal weight matters clinically

Several classes of drugs are dosed based on ideal body weight rather than total body weight, because they distribute primarily in lean body mass:

Gentamicin, Tobramycin (aminoglycosides): maintenance dose calculated using IBW rather than total weight in obese patients. The Devine 1974 paper that introduced the IBW formula was specifically for gentamicin dosing, where total-weight dosing in obesity causes supratherapeutic peak levels.

Acetaminophen: the FDA 2011 advisory recommended IBW-based dosing in patients >50 kg to standardise recommendations.

Anesthetic drugs: Propofol, Thiopental, Rocuronium — IBW-based dosing in obese patients to avoid overdose. Recent studies 2018–2024 show AdjBW (adjusted body weight = IBW + 0.4 × (actual − IBW)) gives better dosing than IBW alone for moderate obesity.

Contrast dye (radiology): many contrast agents are dosed by IBW or Lean Body Mass (LBM, calculated from DXA scan or Janmahasatian formula), not total weight.

The clinical importance of the IBW formula remains substantial even today, despite its limitations as a general-purpose fitness target.

Related Health & Fitness Calculators

Ideal body weight is one input to weight planning; the other tier-2 tools in this cluster support body composition, energy budget, and pregnancy lifecycle goals:

Body Fat Calculator — the IBW-to-lean-mass ratio vs actual fat mass determines whether a patient needs to lose fat, gain muscle, or both.
BMR Calculator — once you have a target weight, BMR × activity multiplier gives a calorie range for safe progress (–500 kcal/day for loss, +500 for gain).
Water Intake Calculator — healthy-BMI-range weight is the variable used in the IOM/EFSA 35 mL/kg heuristic.
Due Date Calculator — pregnancy weight-gain ranges are tied to pre-pregnancy BMI; ideal-weight planning helps set expectations.

Foundational references: Devine 1974 (gentamicin dosing study), Robinson 1983, Miller 1983, Metropolitan Life Insurance 1959, Global BMI Mortality Collaboration 2016 (Lancet meta-analysis of 10.6M subjects), and WHO 1995 / WHO 2004 Asian BMI cutoffs.