Two measurements and one division. The line most people are looking for is 0.5.
Estimates are for general guidance only and are not medical advice. For a personalised plan, book a free guided tour at RPM Gym.
The headline is your waist divided by your height, both in the same unit. Under it sit the three published boundaries, which side of them you are on, and — the row most people actually use — half your height in centimetres, so you can hold the tape against a number rather than a ratio.
0.5 is the boundary that carries the guidance, and it has a plain-English form that survives being repeated: keep your waist under half your height. At 178 cm that means under 89 cm. The ratio and the centimetre figure are the same statement, and the second one is easier to act on in a changing room.
What the boundary is not is a diagnosis. It was drawn across populations as a screening line, which means it is useful for deciding whether to look closer and useless for deciding what is wrong. A reading of 0.52 does not describe a condition, and 0.48 does not rule one out.
The reason the ratio earns its place next to weight is that it needs no scale and no chart. Two people at the same weight and height can carry it very differently, and the tape sees that where the scale cannot.
| Below the lowest boundary | under 0.40 | Below where the published chart starts. It means the tape is reading small against your height, and this page will not tell you what to do about that — a low reading has too many explanations, from build to illness, for a ratio to choose between them. |
|---|---|---|
| Within the chart's OK zone | 0.40 – 0.49 | Your waist is under half your height, which is what the guidance asks for. Nothing here says anything about the rest of your health, because nothing here measured it. |
| Above the 0.5 boundary | 0.50 – 0.59 | Past the boundary the guidance names. What that warrants is a closer look rather than a conclusion, and the closer look is a person with a stethoscope, not a second calculator. |
| Above the 0.6 boundary | 0.60 and over | Past the chart's upper boundary. Same reading as above, further along: it is a screening result and the next step is a clinician, not a diet decided by a website. |
Ratio = waist ÷ height, both in centimetres Half your height = height ÷ 2 Boundaries: 0.4, 0.5, 0.6. The 0.5 boundary is the one the guidance is written around. No adjustment for sex, age, ethnicity or build. The ratio is the ratio.
A man of 178 cm with a 92 cm waist, measured at the navel after breathing out.
0.52, and 3 cm over half his height. Those are the same fact said twice, and the second version is the one worth carrying around — 3 cm is a thing a tape can find again in six weeks. What neither version is is a verdict: it is a screening reading that says look closer, and looking closer is somebody else's job.
The guidance is to keep your waist under half your height, which is a ratio under 0.5. It is worth being precise about what that number is: a screening boundary set across populations, not a target with health on one side of it and illness on the other. Where you sit relative to it tells you whether looking closer is worthwhile, and that is genuinely all.
The two common conventions are at the navel, or midway between the lowest rib and the top of the hip bone. Both are defensible and they do not give the same number. Pick one, note it, and use it every time — consistency between your own readings matters far more than which convention you chose.
It answers a different question with a different instrument. BMI compares weight to height and cannot see where the weight is; this compares waist to height and cannot see weight at all. The ratio's practical advantage is that it needs no scale and its boundary is memorable. That is not the same as one replacing the other.
Because the published boundaries do not. Ashwell's values are deliberately one rule for everyone, and the simplicity is the argument for them — a boundary you can remember is a boundary people use. Adding a sex adjustment here would mean inventing one, and an invented adjustment is worse than a blunt rule that says what it is.
This page will not tell you that, and the previous version of it did, which was wrong. A reading below the chart's lowest boundary has too many explanations — a light build, a long torso, a mismeasurement, or something that needs a doctor — and a tape measure cannot distinguish between them. If it is unexpected or you feel unwell, that is a question for a clinician.
Not at all, as long as both numbers are inches. The units cancel in the division, which is exactly why the ratio travels so well. What does break it is mixing units, and nothing in the arithmetic can catch that — a height in inches against a waist in centimetres returns a confident, meaningless number.
Six weeks of steady training moves the waist and the weight at different speeds, and it is normal for one to sit still while the other does not. If you would rather have someone read both numbers with you than guess, the guided tour at Al Manhal is free.