What is ideal body weight used for?

Ideal body weight is a height-based estimate used to dose drugs whose distribution does not track total body weight, such as aminoglycosides and vancomycin, and to set lung-protective tidal volumes (typically 6 to 8 mL per kg of IBW) during mechanical ventilation.

What is the Devine formula?

The Devine formula is the clinical standard. For men it is 50 kg plus 2.3 kg for every inch of height over 60 inches; for women it is 45.5 kg plus 2.3 kg per inch over 60. It was originally derived for drug dosing and remains the most cited version.

How does Robinson differ from Devine?

The Robinson formula uses a lower per-inch slope: 1.9 kg per inch for men and 1.7 kg for women, with base weights of 52 and 49 kg. It tends to give slightly lower estimates than Devine, especially in taller patients, and is one of several published alternatives.

What about patients shorter than 60 inches?

The formulas were validated for heights of about 60 inches and above. Below that the linear term turns the estimate downward, so this tool floors the result at the base weight to avoid an unrealistically low figure. Use clinical judgement for very short adults.

Should I dose by ideal or actual weight?

It depends on the drug. Hydrophilic drugs that stay in lean tissue are often dosed on ideal weight, while in obese patients an adjusted body weight is frequently used instead. Always check the specific dosing guidance for the medication.

Ideal Body Weight Calculator (Devine & Robinson)

Ideal body weight is a height-based weight estimate that clinicians use when total body weight would give the wrong answer. Many drugs distribute mainly into lean tissue rather than fat, and modern ventilation targets tidal volumes scaled to a patient’s predicted lean size, so a reliable IBW figure underpins safe dosing.

How it works

Both formulas take height in inches and build up from a sex-specific base weight at 60 inches (152.4 cm):

Devine male:    50.0 + 2.3 x (height_in - 60)
Devine female:  45.5 + 2.3 x (height_in - 60)
Robinson male:   52.0 + 1.9 x (height_in - 60)
Robinson female: 49.0 + 1.7 x (height_in - 60)

The tool accepts height in centimetres and converts to inches before applying the equations. Below 60 inches the estimate is floored to the base weight.

Example and notes

A 175 cm man is about 68.9 inches tall, so the Devine IBW is 50 + 2.3 x 8.9, roughly 70.4 kg, while Robinson gives about 68.9 kg. Use IBW for lung-protective tidal volume targets and for hydrophilic drug dosing, and switch to an adjusted body weight in markedly obese patients where ideal weight would under-dose.