Ideal Body Weight Calculator

What is ideal body weight?

Ideal body weight (IBW) formulas estimate a weight considered appropriate for a given height and sex. Clinicians use IBW for drug dosing, ventilator tidal volume settings, nutritional targets, and as a rough screening reference, not as a mandatory goal weight for every individual.

No single formula is universally correct.

Frame size, muscle mass, ethnicity, age, and health conditions all influence what weight is optimal for a person. The four classic formulas (Devine, Robinson, Miller, and Hamwi) often disagree by several kilograms for the same person. This calculator displays all four results plus their average so you can see the range of estimates rather than relying on one number alone. Dietitians calculating enteral feeding goals in obese ICU patients may use adjusted or ideal weight so protein grams stay practical. Clinical dosing often documents which IBW formula the institution defaults to in the electronic health record. Muscular patients should compare IBW with body fat percent before choosing a weight loss goal tied to formula output.

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The four IBW formulas explained

Devine (1974): Men IBW (kg) = 50 + 2.3 × (height in inches - 60). Women: 45.5 + 2.3 × (height in inches - 60). Originally developed for gentamicin dosing. Robinson (1983): Men = 52 + 1.9 × (height in inches - 60). Women = 49 + 1.7 × (height in inches - 60). Robinson produces slightly lower estimates than Devine for many heights.

Miller (1983): Men = 56.2 + 1.41 × (height in inches - 60). Women = 53.1 + 1.36 × (height in inches - 60). Hamwi (1964): Men = 48 + 2.7 × (height in inches - 60). Women = 45.5 + 2.2 × (height in inches - 60). Hamwi is one of the oldest clinical references still in use.

All formulas assume height above 5 feet (60 inches). For heights below that threshold, results should be interpreted cautiously.

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Adjusting for frame size

People with larger skeletal frames can healthily carry more weight than formulas predict. Clinical practice sometimes adjusts IBW by ±10% for small or large frame size, determined by wrist circumference relative to height.

Athletes with substantial muscle mass often weigh well above IBW while maintaining low body fat and good metabolic health. IBW was never intended to label muscular individuals as overweight. Older adults may benefit from weights slightly above traditional IBW to protect against sarcopenia and frailty.

Geriatric guidelines sometimes favor BMI 23 to 30 over strict adherence to formula outputs.

[2][4]

Why formulas disagree

Devine created his formula for gentamicin dosing in the 1970s. Robinson and Miller re-fit similar linear height relationships with different intercepts and slopes, producing spreads of 3 to 6 kg for typical adults.

Hamwi equations predate modern obesity prevalence and can feel low for large-framed or muscular people.

Hospital electronic health records often default to Devine while nutrition software prefers Robinson. Showing all four outputs highlights uncertainty. Geriatric patients may need weights above formula outputs to prevent sarcopenia; pediatrics requires entirely different growth charts, not these adult lines.

[1][2][3]

Clinical uses of ideal body weight

Aminoglycoside antibiotics, chemotherapy agents, and some sedatives are dosed using IBW or adjusted body weight when patients exceed ideal weight significantly.

Nutrition support teams use IBW to calculate protein and calorie targets in hospitalized patients where actual weight reflects fluid retention or obesity. If you are using IBW for personal weight loss goals, treat it as one data point alongside BMI, body fat percentage, waist circumference, and how you feel and function at different weights. Pediatric ideal weight uses growth charts, not Devine-style linear equations meant for adults over five feet tall.

Print all four formula outputs when discussing weight goals with your care team so everyone sees the same spread. Robinson IBW often runs 1 to 3 kg below Devine for women of average height, which matters when gentamicin dosing uses institution-specific defaults. Hamwi outputs can exceed Miller for tall men because the slope on height inches is steeper in the Hamwi male equation.

[1][3]

Where the ideal body weight formulas came from

Ideal body weight is a historical label for several height-based reference equations. Hamwi presented a bedside rule in 1964. Devine published his equation in a 1974 gentamicin dosing discussion. Robinson and Miller proposed alternatives in 1983. None of the four measured an individual's optimal fat mass, function, or long-term health outcome.

For a 5 ft 8 in man, the height increment is 8 inches. Devine gives 50 + 2.3 × 8 = 68.4 kg. Robinson gives 52 + 1.9 × 8 = 67.2 kg. Miller gives 56.2 + 1.41 × 8 = 67.5 kg. Hamwi gives 48 + 2.7 × 8 = 69.6 kg. The 2.4 kg span is a formula-choice effect, not uncertainty that can be eliminated by more precise height measurement.

A modern analysis found differences from Devine as large as 14% for men and 19% for women across examined heights. Peterson and colleagues proposed a universal BMI-based equation because the old linear formulas behave inconsistently at short and tall heights. Clinical protocols still use legacy equations because dosing studies and workflows named them, not because one defines a universal healthy weight.

[1][2][3][5][6]

How to use the ideal body weight calculator

Measure standing height without shoes against a wall or stadiometer.

Select the formula only if your medication reference, ventilation protocol, or clinician names one. If no method is specified and you are exploring personal weight, read the outputs as historical comparison values rather than targets. Review the spread instead of averaging automatically. A protocol that requires Devine should receive the Devine result, not the average of four formulas.

For a general health discussion, compare the estimates with BMI range, waist measurement, body composition, medical history, and a weight you can maintain while functioning well. Do not calculate a prescription dose or ventilator setting from this page. Drug selection, renal function, therapeutic monitoring, and protocol-specific caps can matter more than the reference weight. Lung-protective ventilation uses predicted body weight equations tied to height and sex, which should not be casually substituted with every equation labelled IBW.

[6][7]

IBW compared with BMI ranges and body composition

A BMI-based healthy-weight range provides a band rather than one point. At 1.73 m, BMI 18.5 to 24.9 corresponds to about 55.4 to 74.5 kg, a much wider interval than the spread among legacy IBW equations.

That range still does not measure fat distribution or distinguish muscle from fat.

DXA, waist circumference, and functional measures answer different questions. A strength athlete may exceed every IBW output because of muscle. A person can match an IBW value while carrying high abdominal fat or having low muscle. The appropriate comparison depends on whether the question concerns drug distribution, cardiometabolic screening, nutrition, or appearance. Frame-size adjustments of plus or minus 10% appear in older nutrition practice, but the exact percentage is not a measured correction for an individual. Wrist and elbow breadth can describe skeletal size, yet they do not validate a new personal ideal. Use composition and health outcomes when a legacy result conflicts with the person in front of it.

[4][5][8]

Who should not treat IBW as a goal

The common equations were built for adults and usually start at 5 feet. Children need age- and sex-specific growth charts. Pregnancy requires gestational weight-gain guidance based on pre-pregnancy BMI.

Amputation, edema, ascites, spinal deformity, and inability to measure standing height require specialized clinical methods.

Older adults with sarcopenia can fall below a formula result without benefiting from deliberate weight gain to that number, or sit at the result while losing muscle. Forced weight loss toward IBW can worsen frailty. Clinicians assess weight trend, intake, strength, disease burden, and function. If a calculated value would require a large weight change, set an initial health target with a clinician. Guidelines often begin with a 5% to 10% reduction for adults with overweight or obesity when weight loss is indicated. That outcome-based goal has a different purpose from matching an old dosing equation.

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How it works

Devine (1974), Robinson (1983), Miller (1983), and Hamwi (1964) formulas each use height above 5 feet with sex-specific constants.

Frequently asked questions

• Which IBW formula is best?No single formula is perfect. Averaging all four gives a reasonable estimate. Frame size and muscle mass also matter.

Related calculators

References

1. Devine, 1974. Gentamicin therapy
2. Robinson et al.. Ideal body weight: a new look at an old formula
3. Miller et al.. Ideal body weight in men and women
4. CDC. About Adult BMI
5. Peterson et al.. Universal equation for estimating ideal body weight and body weight at any BMI
6. Walter & Patel. Variability in ideal body weight formulae
7. ARDS Network. Ventilation with lower tidal volumes for acute lung injury and ARDS
8. Pai & Paloucek. The origin of the ideal body weight equations
9. Jensen et al.. Managing overweight and obesity in adults: 2013 guideline executive summary