What is a healthy weight for your height?

"What should I weigh?" is a reasonable question that does not have a single-number answer. What it has is a range — and knowing where the range comes from tells you quite a lot about when to take it seriously and when to ignore it.

The short answer: a range, not a number

For adults, the reference range is a body mass index between 18.5 and 24.9. Turned back into kilos, that is a span of roughly 15–22 kg for most adult heights.

Notice how wide those are. At 175 cm, anything from 56.7 to 76.3 kg sits inside the range — a difference of nearly 20 kg. Two people at opposite ends of it look completely different and are both, on this measure, unremarkable.

That width is the honest part of the answer. Anyone who gives you one number for your height has narrowed a range to a point, and the point they chose was arbitrary.

How BMI is worked out

Weight in kilograms divided by height in metres squared.

To go the other way — from a height to a weight range — multiply height in metres squared by each end of the range. At 168 cm: 1.68 × 1.68 = 2.82, so 18.5 × 2.82 = 52.2 kg and 24.9 × 2.82 = 70.3 kg.

That is the entire calculation. It uses two facts about you and nothing else, which is both why it is used everywhere and why it is limited.

What the bands mean, and what they do not

These bands were built to describe populations. They are genuinely useful for that: if you want to know how a country's weight is changing over thirty years, BMI collected from a hundred thousand people will tell you.

Applied to one person standing on a scale, the same number carries much less. It does not know whether your weight is muscle or fat. It does not know where the fat is, which matters. It does not know your blood pressure, your blood sugar, how well you sleep or how far you can walk — all of which describe your health more directly than your weight does.

So: a useful prompt, a poor verdict. If your BMI has moved from 24 to 29 over five years, that is worth paying attention to. If it reads 26 and you are strong, active and well, that is a number, not a problem.

Five cases where BMI is a poor guide

If you carry a lot of muscle

Muscle is denser than fat. Someone who has trained seriously for years can read comfortably into the overweight band with low body fat. The measure is simply being asked a question it cannot answer.

If you are under 18

The 18.5 and 24.9 cut-offs are adult figures. For children and teenagers, BMI is compared against growth charts for their age and sex. This is why our calculator shows under-18s their BMI and their maintenance calories, and then stops — no band, no weight range, no calorie target.

If your background suggests different thresholds

Several health authorities use lower BMI thresholds for people of South Asian, Chinese and some other backgrounds, because body composition at a given BMI differs between populations. In a country where a large share of residents fall into those groups, that is a real consideration and a good question to put to a doctor or dietitian.

If you are pregnant

BMI is not interpreted in the usual way during pregnancy, and weight targets are set with a midwife or doctor.

If you are older

Muscle mass tends to fall with age and height can decrease, both of which shift BMI without much change in body fat. Above about 65, the range is generally read more loosely.

Two measurements that tell you more

Neither needs equipment beyond a tape measure.

• Waist circumference. Measured at the midpoint between the lowest rib and the top of the hip bone, on bare skin, at the end of a normal breath out. Where fat sits matters, and this measures it directly. It is also the number that tends to move first when someone starts training, which BMI often does not.
• Waist-to-height ratio. Waist divided by height, both in the same units. A commonly cited rule of thumb is to keep your waist under half your height — at 170 cm, under 85 cm. It is a single figure, it needs no chart, and it accounts for the fact that a 90 cm waist means something different on a tall person.

Track one of these alongside your weight and the picture gets much clearer, particularly in the weeks when the scale sulks and your waistband does not.

What to actually do with it

If you are above the range and want to move down through it, the mechanism is the same regardless of what the band is called: eat somewhat less than you burn, keep protein high enough to hold on to muscle, and give it months rather than weeks. How many calories to eat a day has the arithmetic, and how much protein you need has the other half of it.

And do not set the top of the range as a finish line. Most of the benefit people notice — energy, sleep, how stairs feel, blood markers if they are being tracked — arrives in the first several kilos, long before any band changes. That is a much better thing to aim at than a number on a chart.