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What does ideal weight mean?
Ideal weight is not a single figure, it is a range. At the same height, two healthy people can differ by ten kilograms, depending on muscle mass, frame width and age. That is why the calculator shows you a range first, not a number.
The single figure from the Devine formula appears below it, as a landmark. It is useful when someone needs one number, such as when a drug dose is calculated. It is not a target you have to reach.
How is the healthy weight range calculated?
The range comes from BMI (body mass index), worked backwards. Height in meters is multiplied by itself, and the result is multiplied once by 18.5 and once by 24.9. The two figures are the ends of the normal weight range of the World Health Organization [1].
For example, at 1.75 m the range runs from 56.7 kg to 76.3 kg. You can check any weight in this range with the body mass index calculator. The range has the same limits as BMI, so it cannot be applied in children, in athletes, in pregnancy or in older people.
What is the Devine formula and what is it used for?
The Devine formula was published in 1974, for antibiotic dosing [2]. It starts from 50 kg in men and 45.5 kg in women, for a height of 152 cm, then adds 2.3 kg for every extra 2.54 cm. It is still used today in pharmacology, where the dose of many drugs is referred to a theoretical weight, not to the real one.
For a person who wants to know what they should weigh, the formula has serious limits. It takes no account of muscle mass, it gives different figures for men and women of the same height, and it drops to unrealistic values below 140 cm. The ideal weight range above remains the most useful landmark.
What target weight makes sense when you have diabetes?
In a patient with type 2 diabetes, losing 5–10% of current weight improves blood glucose, blood pressure and blood fats. A loss of 15–20% or more can even lead to remission in some patients, especially in the first years after diagnosis.
For someone of 100 kg, that means a first target of 90–95 kg, not 75 kg. A target of 5% weight loss is the easiest to reach, and the benefit is already present there. A weight target too far from the present value discourages and is often abandoned.
Glossary terms used here