Waist-to-height ratio for women

Why your waist matters

BMI knows how much you weigh. It has no idea where that weight sits, and that turns out to matter a great deal.

Fat stored deep inside your tummy, packed around organs like the liver, is known as visceral fat. It's much more closely linked to type 2 diabetes, high blood pressure and heart disease than fat on your hips, bottom or thighs. Two women with an identical BMI can carry very different amounts of it, which is one reason BMI alone can mislead.

That's why, since 2022, NICE has advised that adults with a BMI under 35 should measure their waist-to-height ratio as well. It takes two minutes and a tape measure.

How to measure your waist properly

Most people measure in the wrong place, usually at the narrowest point or wherever their trousers sit. Here's how to get a number you can trust.

1. Measure against bare skin, or over a thin top at most.
2. Find the bottom of your ribs and the top of your hip bones. Your waist, for this purpose, is halfway between the two. For many people that's roughly level with the belly button.
3. Stand up straight with your feet together and breathe out normally. Don't suck your tummy in. Everyone does, and it defeats the point.
4. Wrap the tape round so it's snug but not digging in, and keep it level all the way round. A mirror helps with the back.
5. Measure twice. If the two readings are more than a centimetre apart, do it a third time.

Then measure your height in the same units. Centimetres for both, or inches for both. Mixing them is the one mistake that gives a completely meaningless answer.

What your ratio means

If your ratio comes out below 0.4, that's outside the NICE bands. Look at your BMI as well, and have a chat with your GP if you're worried you might be underweight.

You may also come across fixed waist targets, like keeping your waist under 80 cm (31.5 in) as a woman. Those are still used, but waist-to-height is fairer because it scales with you. An 80 cm waist on a 5ft woman and on a 5ft 10in woman are not the same thing.

The string test

No tape measure? Cut a piece of string the same length as your height. Fold it in half. Now wrap it round your waist at the point described above.

If the two ends meet or overlap, your waist is less than half your height and your ratio is under 0.5. If they don't reach, it's over. It's not precise, but it's a surprisingly good kitchen-table check.

BMI or waist-to-height ratio?

Use both. They answer different questions. BMI is still the standard way to classify weight, and it's what your GP will record. Waist-to-height adds the part BMI can't see.

Where it gets useful is when the two disagree:

• Healthy BMI, ratio above 0.5. This is sometimes called normal-weight central obesity. Your weight looks fine on paper, but you're carrying more around your middle than is ideal. It's worth taking seriously, especially from your mid-40s onwards, when the menopause shifts fat towards the middle.
• BMI in the overweight range, ratio under 0.5. This often means you carry more muscle or store fat lower down. And if you have PCOS, the ratio is worth checking even when your BMI is healthy. Your health risk may be lower than your BMI alone suggests.

One exception: NICE doesn't recommend using waist-to-height ratio if your BMI is 35 or above, because at that point the health risks are already considered high and the extra measurement doesn't add much.