How to measure your waist: the NHS and BHF method, waist to height ratio and when to see a GP

Why measure your waist at all?

Weight and BMI say how much of you there is. They do not say where it sits. The British Heart Foundation (BHF) explains that the size of your waist shows how much fat sits around your belly.² Some of that fat lies under the skin, which is the fat you can feel. Another type, visceral fat, builds up around your organs and is linked to high cholesterol, high blood pressure and type 2 diabetes.²

The BHF also says a larger waist may mean there is too much fat inside organs, such as the liver, which can raise the risk of coronary heart disease and type 2 diabetes.² That is why the NHS pairs BMI with a waist check. After you get a BMI result from the NHS calculator, you may be asked to measure your waist, because it helps show whether you are carrying too much weight around your tummy.³

The NHS BMI calculator cannot tell muscle from fat, so a muscular adult can score high on BMI without much body fat.³ The waist gives a second view. Our guide to BMI and healthy weight covers the BMI side and the weights in stones and pounds.

Which number to use: waist size or waist to height ratio?

You will see two ways of using a tape measure. One looks at the waist alone. The other divides the waist by your height. The BHF says NICE, the National Institute for Health and Care Excellence, recommends the waist to height ratio to find out how much fat is stored around your belly.² The NHS gives a matching rule: try to keep your waist size to less than half your height.¹

The ratio helps because it allows for the fact that taller people have bigger frames. A 34 in waist means something different at 5 ft 2 in than at 6 ft 2 in. The BHF puts it this way: a smaller gap between your waist and your height means your waist is larger.²

The NHS and the BHF both limit the method to adults with a BMI below 35. The BHF says that with a larger body size or an overhanging abdominal fold, it may be hard to place the tape or find the right point.² If you cannot measure accurately or your BMI is 35 or above, the BHF advises speaking to a healthcare professional, who can look at BMI together with an individual assessment, which may include checking blood pressure.²

How to measure your waist, step by step

1. Find the halfway point. Locate the bottom of your ribs and the top of your hips. The midpoint between them is where the tape goes.²
2. Wrap the tape around your belly. Pull it snug but not so tight that it digs into your skin.² Keep the tape level all the way round.
3. Breathe out naturally, then read. Note where the tape meets the zero end. The BHF says the reading can be in inches or centimetres.² Do not suck your tummy in.
4. Measure your height. Use the same unit as for your waist.²
5. Divide your waist by your height. The result is your waist to height ratio.²

Measure against bare skin or thin clothing, standing relaxed with your feet together. Repeat the measurement twice and use the average if the two differ. Measure at a similar time of day, because the tummy changes through the day with meals and drink. Write the number down, with the date, so you can compare in a month.

The string method

If you do not have a tape measure, the BHF describes a string method.² Use string to measure your height from the bottom of your feet to the top of your head, cut or mark it, and fold it in half. Wrap the folded string around your waist. If you cannot completely wrap it round, this suggests you are carrying too much fat around your waist.² It is a rough screen, not a precise number, so treat it as a prompt to measure properly with a tape.

What does your ratio mean?

The two UK sources agree on the key line. The NHS says to keep your waist below half your height, which is a ratio below 0.5.¹ The BHF puts the healthy range at 0.4 to 0.49 and says a ratio of 0.5 or above probably means weight loss would reduce your risk of heart and circulatory disease.²

Waist in inches and centimetres, by height

The ratio is easier to use once you see it as a waist size. The table below multiplies each height by 0.4, 0.5 and 0.6, the band edges given by the BHF.² The 0.5 column is the waist that equals half your height, the line the NHS asks you to stay under.¹

The BHF worked example

The BHF gives an example: a waist of 96.5 cm and a height of 170 cm give 96.5 ÷ 170 = 0.57.² That sits in the 0.5 to 0.59 band. In inches the same person has a waist of about 38 in and a height of about 67 in. The ratio stays the same because both numbers change by the same factor, which is why you can use either unit as long as you do not mix them.

A second example from the NHS rule: someone who is 160 cm tall should aim for a waist below 80 cm, because 80 ÷ 160 = 0.5. Here the arithmetic is mine, the rule is the NHS’s.¹ Someone who is 5 ft 8 in tall (68 in) has half-height at 34 in, as the table shows.

Measure once a month, not every day. Waist size moves slowly, so a change over several weeks is a more useful signal than a difference between two mornings.

Waist, BMI and what to do with both

The NHS says that if your BMI is under 35 you can use the waist to height ratio calculator to help you understand whether you are carrying too much fat around your tummy.¹

That is a practical way to read the two together. A BMI in the healthy range with a ratio of 0.5 or above is worth a conversation with a GP or practice nurse. A BMI above the healthy range with a ratio below 0.5 can happen in people with a lot of muscle, since the NHS notes BMI cannot tell muscle from fat.¹

If you want to lose weight, the NHS suggests steady loss of 1 to 2 lb (0.5 to 1 kg) a week and getting active for 45 to 60 minutes a day, which can be spread across the day.¹ It says losing 5 to 10% of your body weight can improve your health.¹ The BHF also points out that the more excess fat you have around your belly, the higher the ratio.²

What a home scale or tape can and cannot tell you

A tape measure gives you one number at one place. It cannot say whether the fat is under the skin or around your organs. The BHF notes that visceral fat builds up around your organs and is linked to high cholesterol, high blood pressure and type 2 diabetes, but the tape measures the outside only.²

A body composition scale gives you more variables. It estimates fat and muscle from a tiny electrical current passed through the body. The manufacturer’s own page for Vita says readings are estimates that vary with hydration, meals, recent exercise and time of day, and that the scale is not suitable for people with a pacemaker or similar implanted device.⁵ So a scale and a tape are two different tools. The tape is the one the NHS and the BHF use for the ratio.¹²

• Use the tape for waist to height ratio, as the BHF describes.²
• Use the scale for weight and BMI trends, with the same routine each time.
• Treat any fat or visceral fat figure from a scale as an estimate.⁵
• Do not use a ratio if your BMI is 35 or above. Ask a healthcare professional.²

Frequently asked questions