Ideal weight: formulas and healthy weight range

Searching for an “ideal weight” usually means wanting an answer more concrete than a plain BMI figure — a number of kilograms, easier to picture than an index. You can calculate your BMI directly with the calculator on this site, which already shows this healthy weight range for your height. This page explains where that range comes from, then presents three older formulas — Lorentz, Devine and Creff — still widely cited online, together with their real limits.

The WHO healthy weight range: the reference to rely on

The sturdiest reference is not a single figure but an interval: the weight range that corresponds to a BMI between 18.5 and 25, the zone the World Health Organization treats as normal weight (see our full BMI classification chart). This range is calculated directly from height, by multiplying the square of the height in metres by 18.5 for the lower bound, and by 25 for the upper bound.

For someone measuring 1.65 m, for example, this gives a range of roughly 50.4 to 68.1 kg. Any weight inside that interval falls into the normal weight category — it is not the midpoint that counts, but the whole range. This logic, simple and tied directly to the official BMI thresholds, is what this site’s calculator favours over a single isolated figure.

The historical formulas: Lorentz, Devine and Creff

Before BMI became the standard reference, several formulas attempted to estimate an “ideal weight” from height alone, sometimes with age added in. They are still cited today, often without their original context — here are the three main ones.

The Lorentz formula

It expresses a weight based on height alone, with a different constant for men and for women. It is probably the best known of the historical ideal-weight formulas, and one of the oldest still in circulation. Its age partly explains its popularity: simple enough to compute by hand, it served as a default benchmark long before BMI became widespread.

The Devine formula

Originally a clinical tool, it was designed to help adjust certain medication doses to a patient’s weight, not to set a weight target. It also distinguishes men and women, and was historically expressed in pounds and inches above a reference height — a dosing calculation repurposed, over time, as an “ideal weight” benchmark.

The Creff formula

It differs from the two above by including age in the calculation alongside height, which means it requires knowing a person’s age to be applied at all. It is built on the idea that a weight benchmark might shift slightly with age — an intuition that has never replaced the healthy weight range as the main reference.

Historical benchmarks, not targets to hit

These three formulas share the same limitation: built for the adult of typical stature, they take no account whatsoever of body composition. A very muscular person, a slender build, or an unusual stature will, under these formulas, produce a result far removed from what an individual assessment would suggest. None of them measure fat mass or muscle mass — the same restriction covered in our page on the limitations of BMI applies here as well.

In children and teenagers, these formulas make no sense at all: build is instead read using growth percentile charts by age and sex, a subject covered in our guide on BMI for children.

Why the healthy weight range is the better reference

Unlike the historical formulas, the WHO healthy weight range is directly tied to the official BMI thresholds, the same ones detailed on our BMI chart. It does not claim to measure body composition either, but it has the merit of offering an interval rather than a single figure — a more honest way to represent what a weight-to-height ratio can, and cannot, say. It also applies at any adult height, while the historical formulas grow less reliable as stature moves away from the average they were built on.

Reading a result without turning it into a rigid target

Whatever the method used, an “ideal” weight is never a figure to hit to the gram. A person’s weight naturally varies from one day to the next and one season to another, under factors as varied as hydration, hormonal cycle, or simply the last meal. Fixing a single number as a goal mostly invites needless disappointment over fluctuations that are entirely normal. A range, like the one the WHO retains, fits this reality better than an isolated figure. Whatever formula is consulted, none of them replaces individualised advice: build, muscle mass, age and overall health weigh far more than a theoretical figure. A health professional remains best placed to discuss what is right for you.