Your waist can tell you more than the scales. The NHS waist-to-height ratio tool sets one benchmark — keep your waist under half your height — and says the ratio is used alongside BMI. NICE says a waist more than half your height signals greater risk and recommends that adults with a BMI below 35 measure their own. At 170 cm tall, the line is 85 cm. A calculator gives the ratio straight away.
1. Keep your waist under half your height — under 85 cm at 170 cm.
2. Over half signals greater risk (NICE); use it with BMI.
3. Not for under-5s, pregnancy, eating disorders, growth conditions or adults with BMI over 35 (NHS).
Calculator
Updates as you type. Ratio = waist ÷ height, in the same unit. The NHS tool isn’t for children under 5, pregnant people, anyone with an eating disorder or a growth condition, or adults with a BMI above 35. It isn’t a diagnosis.
What the NHS and NICE say
| Type | What the source says | Worth noting (ours) |
|---|---|---|
| Benchmark | Waist under half your height (NHS, NICE) | A ratio under 0.5 (our conversion) |
| Meaning | A waist over half your height signals greater risk (NICE) | Which conditions isn’t on these pages |
| With | Used alongside BMI (NHS) | — |
| Who | Adults with BMI below 35 measuring their own (NICE) | — |
| Not for | Under 5, pregnant, an eating disorder or suspected one, a growth condition, adults with BMI over 35 (NHS) | — |
| Children | 17 or under with a parent or carer; ages 5–17 check BMI first (NHS) | — |
The “half” line by height — our conversion
| Height | Waist line (half height) | Worth noting (ours) |
|---|---|---|
| 150 cm | 75 cm | Stay below |
| 160 cm | 80 cm | — |
| 170 cm | 85 cm | — |
| 180 cm | 90 cm | — |
The lines are height divided by 2 (our conversion). Where to measure is explained step by step inside the NHS tool, which we didn’t set out. Weight is in BMI and calorie calculator; plateaus in diet plateau.
Checklist
- ☐ Height and waist in the same unit
- ☐ Ratio under 0.5 — under half your height
- ☐ Check BMI too
- ☐ Not for pregnancy, under-5s, eating disorders or BMI over 35
- ☐ Worried? Talk to a pharmacist or GP
Questions that remain
Are there bands like 0.6?
The NHS and NICE pages we read give only the “under half” benchmark. The NICE guideline text (NG246) with any bands didn’t open, so we haven’t set it out.
If my BMI is fine, can I skip the waist?
The NHS says the ratio is used alongside BMI, not instead of it.
Sources
- NHS — Calculate your waist to height ratio — source (reviewed 25 February 2025, next review 25 February 2028; checked 19 October 2026). Under-half benchmark, use with BMI, who shouldn’t use it, children.
- NICE — “Keep the size of your waist to less than half of your height” (consultation deadline shown as 11 May 2022). Over half signals greater risk; adults with BMI below 35.
- Not read. NICE NG246 text (didn’t open); where to measure (inside the tool).
- What we added. The “worth noting” column and the Korean everyday gloss.
Where to check further
- A pharmacist or GP — if you’re worried about your waist.
Written on 19 October 2026. The content is from the source; the glosses are ours.
