Ideal Body Weight Calculator (Devine, Robinson, Miller, Hamwi, Broca, Lorentz)

Understanding the ideal body weight calculator — concept and principle

"Ideal body weight" (IBW) is a reference weight for a given height and sex. Clinicians use it to dose some drugs, set ventilator volumes and estimate nutrition needs. No single formula is correct, so this calculator shows seven common ones side by side, from the clinical Devine formula to the simple Broca rule and the weight that matches a BMI of 22.

Each formula adds a fixed amount per inch over 5 feet, so the answers spread over a 67–75 kg band.

How it is calculated

Let inch = height (cm) ÷ 2.54 − 60, the number of inches above 5 feet.

Devine (1974): men 50 + 2.3 × inch; women 45.5 + 2.3 × inch.
Robinson (1983): men 52 + 1.9 × inch; women 49 + 1.7 × inch.
Miller (1983): men 56.2 + 1.41 × inch; women 53.1 + 1.36 × inch.
Hamwi (1964): men 48 + 2.7 × inch; women 45.5 + 2.2 × inch.
Broca: height (cm) − 100.
Lorentz: men height − 100 − (height − 150) ÷ 4; women height − 100 − (height − 150) ÷ 2.
BMI 22 weight: 22 × height (m)².

All results are in kilograms.

The principle

Each formula is a straight line: a base weight at a reference height plus a fixed amount for every extra unit of height. The inch-based formulas come from American clinical practice and life-insurance height-weight tables, which is why they start at 5 feet. Broca's rule from 19th-century France is the simplest version of the same idea. Lorentz adds a correction so that tall people are not given too much weight. The BMI 22 line is different: it scales with height², and 22 sits near the middle of the normal BMI range.

Worked example

Inputs: male, 175 cm. inch = 175 ÷ 2.54 − 60 = 8.898.
Devine: 50 + 2.3 × 8.898 = 70.46 kg. Robinson: 52 + 1.9 × 8.898 = 68.91 kg.
Miller: 56.2 + 1.41 × 8.898 = 68.75 kg. Hamwi: 48 + 2.7 × 8.898 = 72.02 kg.
Broca: 175 − 100 = 75 kg. Lorentz: 175 − 100 − 25 ÷ 4 = 68.75 kg.
BMI 22: 22 × 1.75² = 22 × 3.0625 = 67.38 kg.

Each point is the calculator re-run with only “Height (cm)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Height (cm)	Devine
43.8	-48.38
87.5	-8.77
131	30.85
175	70.46
219	110.08
262	149.7
350	228.93

How to read the result

The formulas spread from about 67 to 75 kg for this person, which shows how uncertain the idea of one ideal weight is. Treat the cluster in the middle (about 68–72 kg) as a reasonable reference and compare it with the healthy BMI range for your height. Clinicians mostly use Devine for dosing; for everyday goals, a range is more useful than a single number.

Common mistakes

Using the inch-based formulas below 152.4 cm (5 feet), where "inch" becomes negative and results are poor.
Treating IBW as a weight you must reach; it ignores muscle, frame size and age.

Keep in mind: These formulas were designed mainly for drug dosing and population reference, not for diagnosing over- or underweight. They are not a diagnosis; ask a doctor or dietitian for a personal target.

Frequently asked questions

Which formula is the most accurate?

None is accurate for an individual. Devine is the clinical standard for dosing; the others differ by a few kilograms.

What is the modified Broca formula?

(Height − 100) × 0.9, a version widely used in Korea that gives lower values than plain Broca.

Does age change ideal weight?

These formulas ignore age. Body composition does change with age, so use them only as rough guides.

Sources: Devine BJ, Gentamicin therapy, Drug Intelligence and Clinical Pharmacy 8 (1974) 650–655 · Pai MP, Paloucek FP, The origin of the "ideal" body weight equations, Annals of Pharmacotherapy 34 (2000) 1066–1069

Checked 8 Nov 2026. Published formulas cited on the page. For information only — not medical advice.

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