Ideal Weight vs Healthy Weight Range

We publish two calculators that look like they answer the same question. They don't, and the difference between them is worth understanding — because one is built on population health evidence and the other isn't.

Two different answers

For someone 170 cm tall:

The single figures sit comfortably inside the range, which is reassuring — but notice how much room the range has. A healthy weight for that height spans nearly 20 kg, and the "ideal" number is one point inside a wide band, not the centre of a narrow one.

Why the range has better foundations

The healthy weight range is a direct inversion of the WHO BMI classification. It takes the normal BMI band and solves for weight at your height:

low  = 18.5 × height(m)²
high = 24.9 × height(m)²

Those cutoffs come from population studies linking BMI bands to health outcomes across very large groups. The range inherits that evidence base directly, which is why we label it high confidence.

The Devine formula, by contrast, was built for drug dosing in 1974 and was never validated against health outcomes — see how ideal weight is calculated. It is labelled moderate confidence for exactly that reason.

A range is the more honest shape

Beyond the sourcing, a range is simply a better fit for the underlying reality. There is no single weight at which health switches on. There is a band within which risk is statistically lower, with soft edges.

A single "ideal" number implies a precision that nobody has demonstrated, and it invites a kind of thinking — being 3 kg "over ideal" — that the evidence does not support.

The regional wrinkle

The healthy weight range also adapts to population, which the Devine formula cannot. Under the WHO Asian cutoffs applied on our India pages, the upper bound for a 170 cm person is 66.2 kg rather than 72.0 kg, because the normal BMI band tops out at 22.9 instead of 24.9.

Same height, same formula structure, different evidence-based cutoff. Why India uses different BMI cutoffs explains the reasoning.

What to actually use

• For a target to think about, use the Healthy Weight Range Calculator. It is better sourced and honestly shaped.
• For a quick clinical reference point, the Devine number is fine, as long as you read it as a reference rather than a goal.
• For context on either, neither accounts for build — see why ideal weight ignores your build and check body fat if you carry above-average muscle.

The bottom line

The healthy weight range is derived from WHO cutoffs validated against health outcomes; "ideal weight" comes from a 1974 drug-dosing heuristic. When they disagree, trust the range — and remember that a wide healthy band is the accurate picture, not a vague one.