Ideal Body Weight Formula: Hamwi, Devine, Robinson, and Miller Explained

Last updated: May 2026

Four primary formulas are used to calculate ideal body weight (IBW): Hamwi (1964), Devine (1974), Robinson (1983), and Miller (1983). All use the same structure — a base weight at 5 feet plus an increment per inch over 5 feet — but with different values. Here’s how each one works and what they’re used for.

The Four IBW Formulas at a Glance

Sample IBW Calculations by Formula (5’10” Male)

The four formulas produce results in the range of 155–165 lbs for a 5’10” man — all within the healthy BMI range of 131–177 lbs for that height, and toward the lower-middle of it.

Each Formula Explained

Hamwi Formula (1964) — G.J. Hamwi

The oldest and most commonly memorized IBW formula. Dr. G.J. Hamwi developed it in 1964 originally to estimate desirable body weight for calculating insulin doses for diabetic patients — not as a weight loss goal or appearance standard.

US customary version:

• Men: 106 lbs for the first 5 feet + 6 lbs for each additional inch
• Women: 100 lbs for the first 5 feet + 5 lbs for each additional inch
• Adjust ±10% for small or large frame

This is sometimes called the “100 + 5 rule” (women) or “106 + 6 rule” (men). It’s the easiest to calculate mentally — no calculator required. For a 5’8″ woman: 100 + (5 × 8) = 140 lbs (medium frame).

Devine Formula (1974) — B.J. Devine

The most widely used IBW formula in clinical medicine. Dr. B.J. Devine published it in 1974 in a paper on gentamicin dosing — like Hamwi, it was designed for medication dosing, not fitness goals. It became the standard because it was simple and widely adopted by pharmacists and clinicians.

Formula:

• Men: 50.0 kg + 2.3 kg per inch over 5 feet
• Women: 45.5 kg + 2.3 kg per inch over 5 feet

Note that the Devine formula uses the same increment (2.3 kg/inch) for both men and women — only the base weight differs. This is its primary distinction from Hamwi, which uses different increments by sex.

The Devine formula is used by MDCalc and is the standard reference for IBW in most clinical dosing guidelines, ventilator tidal volume calculations, and fluid management protocols.

Robinson Formula (1983) — J.D. Robinson

A modification of the Devine formula published by J.D. Robinson in 1983. Robinson’s work found that Devine’s formula slightly overestimated IBW for taller individuals and proposed different base values:

Formula:

• Men: 52 kg + 1.9 kg per inch over 5 feet
• Women: 49 kg + 1.7 kg per inch over 5 feet

The Robinson formula produces slightly lower IBW values than Devine, particularly for taller individuals. Less commonly used in clinical practice than Devine.

Miller Formula (1983) — D.R. Miller

Also published in 1983, also a modification of Devine. The Miller formula has the highest base weight but the smallest per-inch increment, producing the lowest IBW for very tall individuals and the highest for shorter individuals:

Formula:

• Men: 56.2 kg + 1.41 kg per inch over 5 feet
• Women: 53.1 kg + 1.36 kg per inch over 5 feet

Clinical Applications of IBW Formulas

IBW formulas were developed for clinical use, not fitness goals. Their primary applications:

• Medication dosing: Many drugs (aminoglycosides, vancomycin, certain chemotherapy agents) are dosed by IBW rather than actual weight because drug metabolism correlates better with lean mass
• Ventilator management: Tidal volume during mechanical ventilation is calculated using IBW (typically 6–8 mL/kg IBW) to prevent ventilator-induced lung injury
• Fluid management: Maintenance fluid calculations in hospitalized patients often reference IBW
• Adjusted body weight: For obese patients, an adjusted body weight (IBW_adj) is used: IBW + 0.4 × (Actual Body Weight − IBW)

Limitations of IBW Formulas

• All four formulas only consider height and sex — they ignore muscle mass, body fat, bone density, and frame size
• They produce a single number rather than a range, which can be misleading given natural body diversity
• Formulas produce IBW values that are often at the lower end of the healthy BMI range — they were not designed to define an “optimal” weight for wellness or performance
• None were validated against health outcomes — they were validated against drug metabolism and fluid dynamics
• A highly muscular 5’10” man may have an actual body weight 20–30 lbs above his IBW and still be metabolically healthy with low body fat

Frequently Asked Questions

Which IBW formula is most accurate?

No formula is definitively more accurate for all individuals — they were designed to approximate the average, not calculate individual health. The Devine formula is most widely used in clinical settings. For fitness purposes, the healthy BMI range (18.5–24.9) gives a more appropriate window than any single-number formula.

Is IBW the same as ideal weight for fitness?

No. IBW is a clinical reference for medical calculations. For fitness and body composition goals, body fat percentage is a more relevant target than any IBW formula, particularly for athletes who may healthily exceed IBW due to muscle mass.