Healthy Weight Calculator

low = 18.5 × height (m)² · high = 25 × height (m)² · gap = low − weight if you are under it, high − weight if you are over it, otherwise 0

height

Standing height, in metres — 170 cm is 1.70 (m)

weight

The weight you are at today, in kilograms (kg)

low

The bottom of the healthy range: the 18.5 line carried back into kilograms (kg)

high

The top of the healthy range. It is the 25 line on the WHO scale, and the 24 line on the Chinese scale, so it is lower for readers of the Chinese page (kg)

Use it when you want a direction and a distance rather than a category name. It is the right page when you are inside the range and wondering whether a few kilograms matter, when you are outside it and want to know how far, or when you are planning a target and want to see what the band says before you pick a number. If what you actually want is the BMI category you fall into, use the BMI calculator; if you want a clinical formula's target weight, use the ideal weight calculator. This page deliberately prints no BMI at all, because that number already has a page.

1. 170 cm, 70 kg

   1. Height in metres: 1.70, so height squared is 2.89
   2. Low end: 18.5 × 2.89 = 53.5 kg
   3. High end: 25 × 2.89 = 72.2 kg
   4. 70 kg sits inside 53.5 to 72.2, so the gap is 0

   Zero is the answer this page wants to give. The range is wide on purpose — 53.5 to 72.2 kg is nearly nineteen kilograms, and every one of them is inside the line.

2. 165 cm, 45 kg

   1. Height in metres: 1.65, so height squared is 2.72
   2. Low end: 18.5 × 2.72 = 50.4 kg
   3. High end: 25 × 2.72 = 68.1 kg
   4. 45 kg is below the low end, so the gap is 50.4 − 45 = 5.4 kg to gain

   The sign is the whole point: the same page returns a positive number here and a negative number for someone above the range, and the two are not the same kind of problem.

The range is two straight lines drawn from two population cut-points, and it says nothing about how your weight is made up. Two people at the same height and the same weight can be inside it with very different amounts of fat and muscle, which is exactly the gap the body fat calculator and the waist measurements exist to fill. The lines were drawn for adults of European descent, and the Chinese scale used on the Chinese version of this page is a different judgement rather than a translation — a weight that reads as inside the range on one is outside it on the other, and neither is wrong. The band is not a target for pregnancy, for children and adolescents, for athletes carrying a lot of muscle, or for anyone whose clinician has given them an individual range; in those cases the number this page prints is a population average wearing the clothes of an answer. And a gap of a few kilograms at either end is well inside the noise of a bathroom scale.

What is a healthy weight for my height?

On the WHO lines it is whatever falls between a BMI of 18.5 and a BMI of 25 — at 170 cm that is 53.5 to 72.2 kg, and at 165 cm it is 50.4 to 68.1 kg. The Chinese scale used on the Chinese version of this page draws the top line at 24 instead of 25, so the same height gives a lower high end. Both bands are wide by design: the cut-points are meant to sort populations, and a person's position inside the band carries almost no information.

How is this different from the BMI calculator?

Both start from the same two cut-points, and the BMI calculator is the one that prints your index and puts a category name on it. This page skips the index and keeps the band, then subtracts: what it hands back is the distance between your weight and the nearest edge, signed so you can see which direction it is. If you already know your BMI and want the category, that page is faster; if you want to know how much a change would take, that is this one.

How is it different from the ideal weight calculator?

The ideal weight calculator prints targets from three clinical formulas — Devine, Robinson and Miller — and each of them returns a single number that is not a boundary of anything. This page prints the boundaries themselves, which is why the two pages can disagree without either being wrong: a formula's target usually sits a little below the top of the healthy band, not on it.

Why is the healthy weight range so wide?

Because weight for height is a crude measure and the cut-points had to work across a whole population. Nineteen kilograms at 170 cm is not a loophole; it is the range within which the evidence does not distinguish between people on this measurement alone. That is also why the range is only ever a starting point: waist circumference, body fat and how the weight has changed over time all carry information that a height and a weight cannot.

My weight is just outside the range — how worried should I be?

A small distance past either edge is not a diagnosis, and the further you are from the line the more it means. Population risk rises across a band as BMI climbs rather than switching on at a threshold, so a kilogram over the top is a different situation from twenty kilograms over it. The useful move is to look at the trend and at the other measurements rather than at a single crossing, and to treat the band as the thing your target should sit inside rather than as something you have failed.

• Obesity: preventing and managing the global epidemic (WHO Technical Report Series 894) — World Health Organization
• Body Mass Index (BMI) — healthy weight — US Centers for Disease Control and Prevention