BMI gets all the attention, but there's a number some researchers say predicts certain health risks better - and it takes about ten seconds and a tape measure. It's your waist-to-height ratio, and the rule is delightfully simple: keep your waist under half your height. Here's why it works and how to check yours.
The half-your-height rule
Waist-to-height ratio is your waist measurement divided by your height, in the same units. The target is simple: a ratio under 0.5 - in other words, keep your waist less than half your height. The NHS hosts a calculator built on exactly this rule and positions it as a measure to use alongside BMI. You can find yours on our waist-to-height ratio calculator.
Why waist matters (the visceral-fat story)
Fat stored around the abdomen - visceral fat - sits around your organs and is more strongly associated with health risks than fat on the hips and thighs. BMI uses only height and weight, so it cannot see where you carry weight. A tape measure can. That's the gap waist-to-height ratio fills, and why it can add information BMI simply doesn't have.
Waist-to-height vs BMI: what the evidence shows
Both are screening tools, not diagnoses. Because it captures central fat, waist-to-height ratio can flag risk that a "normal" BMI misses - and it avoids over-flagging muscular people the way BMI sometimes does. That doesn't make BMI useless; it makes the two a good pair. Use waist-to-height to answer the question BMI can't: where is the weight?
How to measure correctly (the common mistakes)
- Measure around your middle, roughly level with your belly button.
- Breathe out gently first - don't suck in, and don't pull the tape tight.
- Use the same unit for your waist and your height.
The risk bands
| Ratio | What it suggests |
|---|---|
| Below 0.4 | Below the typical healthy range |
| 0.4 to 0.49 | Healthy |
| 0.5 to 0.59 | Increased risk |
| 0.6 and above | Highest risk band |
The NHS notes this measure isn't suitable for children under 18, during pregnancy, or for adults with a BMI over 35. For anyone else it's a quick, useful check - try it here and compare it with your BMI.