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Ideal Body Weight (IBW) Formula Calculator

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Compare height-based Ideal Body Weight (IBW) estimates using the Robinson and Devine formulas. These results are reference calculations, not personal health, nutrition or treatment targets.

Your details

Sex

This calculator is designed for adults aged 18 and over.

Robinson and Devine estimates
71.1 kg – 73.2 kg
Robinson formula estimate
71.1 kg
Devine formula estimate
73.2 kg
Difference between formula estimates
2.0 kg
Arithmetic average of formula estimates
72.2 kg

Reference estimate only. Robinson and Devine are height-based Ideal Body Weight (IBW) formulas. They do not determine a person's healthy, ideal or medically appropriate weight, and they do not account for body composition, muscle mass, age, ethnicity, pregnancy, health conditions or personal goals.

Do not use this result to calculate medication doses, set a calorie target or make treatment decisions.

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How to use this calculator

  1. Choose the sex to use — both formulas use different constants for men and women.
  2. Enter your height, and pick its unit — centimetres, metres, feet, inches, or feet and inches.
  3. Read the Robinson and Devine estimates, the difference between them, and the arithmetic average of the two.

Nothing is submitted anywhere. The calculation runs in the page as you type, and the link in your address bar carries your figures, so it can be shared or bookmarked.

What do I need to enter?

  • Sex — Male or Female. Each formula uses different constants for each.
  • Height — from 130 cm to 220 cm, or the equivalent in metres, feet, inches or feet and inches (the inches box takes 0 to 11). It is the only measurement either formula uses.

What do the results show?

  • Robinson and Devine estimates — the main figure: the lower and higher of the two formula estimates, in kilograms.
  • Robinson formula estimate and Devine formula estimate — each formula's own figure for your sex and height.
  • Difference between formula estimates — how far apart the two figures are, never negative.
  • Arithmetic average of formula estimates — the midpoint of the two. It is a summary of the figures, not a target.

How this calculator works

  • The Robinson and Devine estimates are each calculated independently from your height and sex.
  • The formula difference is the absolute difference between the two estimates — | Robinson estimate − Devine estimate | — so it is never negative and never favours one formula.
  • The arithmetic average is (Robinson estimate + Devine estimate) ÷ 2. It is a mathematical summary of the two figures only, not a clinical recommendation.
  • Both are height-based reference methods with real limitations: they use only height and sex, and ignore body composition, muscle mass, frame size, age, ethnicity and health.

Estimates are calculated internally in kilograms and rounded for display using the site's normal weight rounding (one decimal place for kilograms). The difference and the average are taken from the unrounded values and rounded only at the final display step, so they stay consistent with the figures shown.

What are the Robinson and Devine formulas?

Robinson IBW (men) = 52 kg + 1.9 kg × (height [in] − 60)
  • Robinson (women) = 49 kg + 1.7 kg × (height [in] − 60)
  • Devine (men) = 50 kg + 2.3 kg × (height [in] − 60)
  • Devine (women) = 45.5 kg + 2.3 kg × (height [in] − 60)

Worked example. A 178 cm man is 178 ÷ 2.54 = 70.1 inches tall. His Robinson estimate is 52 + 1.9 × (70.1 − 60) = 71.1 kg, and his Devine estimate is 50 + 2.3 × (70.1 − 60) = 73.2 kg. The formula difference is | 71.1 − 73.2 | = 2.0 kg, and the arithmetic average of the two is 72.2 kg. Neither figure is a target weight — they are two estimates from two formulas, shown for comparison.

What these estimates do not tell you

No single IBW formula defines an individual's medically appropriate, healthy or personally ideal body weight. Robinson and Devine were built for consistent clinical and historical reference figures, not as fitness or health targets.

  • They use only height and sex — not muscle mass, frame size, age or ethnicity.
  • They are not valid for children, teenagers or during pregnancy.
  • They are not a diagnosis, a body-composition assessment or medical advice, and no figure here is a safe, optimal, recommended or target weight.

For a range-based view of a healthy weight at your height, use the healthy weight range calculator. For a comparison across seven height-based formulas, with their range and average, use the ideal weight calculator.

Frequently asked questions

What is an IBW calculator?

IBW stands for Ideal Body Weight — a reference figure estimated from sex and height alone. This IBW calculator is a comparison tool: it shows the Robinson (1983) and Devine (1974) formula estimates side by side, the absolute difference between them, and their arithmetic average. The results are reference calculations, not a personal, healthy or medically appropriate weight.

How are the Robinson and Devine formulas calculated?

Both take a base weight at 5 feet (60 inches) tall and add a fixed amount for every inch above that. Robinson: from 52 kg + 1.9 kg per inch for men, and 49 kg + 1.7 kg per inch for women. Devine: from 50 kg (men) or 45.5 kg (women) + 2.3 kg per inch for both. Each estimate is calculated independently from height and sex.

Why can Robinson and Devine give different estimates?

The two formulas were fitted to different reference populations more than a decade apart, using different constants. Devine (1974) was designed for drug-dosing calculations; Robinson (1983) was a later revision meant to sit closer to observed average weights. Neither is more accurate or more correct than the other for an individual — they are both rough, height-only estimates, which is why this tool shows both rather than picking one.

Is the average my ideal or healthy weight?

No. The figure labelled "arithmetic average of formula estimates" is exactly that — the mean of the two numbers shown, a mathematical summary with no clinical meaning. It is not a recommended, healthy, acceptable, target, correct or ideal weight. No single IBW formula, and no average of them, defines what any individual should weigh.

Can I use this for medication dosing or calorie targets?

No. Do not use these estimates to calculate medication or infusion doses, set a calorie target, or make any treatment decision. Clinical dosing that uses ideal or adjusted body weight is done by a prescriber or pharmacist against the specific drug reference and the patient’s full clinical picture, not from a general-purpose web calculator.

Is the calculator suitable for children, pregnancy, or people with high muscle mass?

No. Both formulas were derived from adult populations and use only height and sex, so they do not apply to children or teenagers, and they are not valid during pregnancy. They also do not account for muscle mass or body composition: a muscular or large-framed person will sit above these estimates without that meaning anything is wrong. This calculator is designed for adults aged 18 and over.

How is this different from the Ideal Weight Calculator?

This page compares two formulas — Robinson and Devine. The Ideal Weight Calculator compares seven height-based formulas (adding Peterson, Miller, Hamwi, Broca and Lorentz), with the range and average across all seven. Both are formula-comparison references, not a health assessment.

Is IBW a medical measurement?

No. It is a population-average estimate from height and sex, not a measurement of your body composition and not an individually tailored target. It does not diagnose anything and it is not medical advice. For a range-based view of a healthy weight at your height, see the healthy weight range calculator.

Last updated 25 October 2026.