The short answer: waist-to-height ratio is your waist measurement divided by your height. The NHS advises trying to keep your waist to less than half your height. It is a simple screening measure, not a diagnosis.
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How it works
You measure your waist and your height, then divide the waist by the height. It does not matter which units you use, as long as both are the same: the ratio comes out identical in centimeters or inches. A ratio of 0.5 means your waist is exactly half your height.
For example, if you are 170 cm tall, half your height is 85 cm. A waist under 85 cm sits below that line, and a waist over 85 cm sits above it.
How to measure your waist
The NHS calculator page says its calculator explains how to measure your waist. The Public Health Agency in Northern Ireland describes the waist as the distance around your abdomen at roughly the halfway point between the bottom of your ribs and the top of your hips. It advises you to stand up straight, breathe out naturally, and keep the tape measure snug around your waist.
Measure the same way each time so you can compare your results. Our waist-to-height ratio calculator page also has a measuring guide.
Why the waist, and not only weight?
The NIDDK, part of the US National Institutes of Health, says that where your body stores fat matters. Extra fat in the upper body, especially around the abdomen, is linked to a higher risk of weight-related health problems.
The NHS says that calculating your waist-to-height ratio can help you understand if you are carrying too much fat around your tummy, and describes it as a way to measure your health alongside your body mass index (BMI).
Why people use it next to BMI
BMI uses only height and weight. The NIDDK notes that BMI does not directly measure the amount of fat in your body, that very muscular people can have a high BMI without much body fat, and that older adults tend to lose bone and muscle and gain body fat, which can raise health risks even when BMI stays the same. A waist measurement adds a second piece of information.
What it can and cannot do
- It gives you a quick, free way to compare your waist with your height.
- It does not diagnose any condition. The NHS says not to use its calculator to diagnose conditions.
- It does not tell you how healthy you are overall. Many other things matter, including how active you are, what you eat and your medical history.
- It depends on a careful measurement. Small differences in how you hold the tape can change the number.
Who should not use it
The NHS says its calculator is not suitable if any of these apply:
- the person is under 5 years old
- you are pregnant
- you have been diagnosed with an eating disorder, or think you may have one
- you have a growth disorder or another condition that affects your height
- your BMI is over 35 (this applies to adults aged 18 and over)
If you are worried about your waist size, the NHS suggests contacting your local pharmacist or GP surgery.
What to realistically expect
Your ratio is a snapshot. It will not change overnight, and a single reading says little. If you choose to track it, measure the same way each time and look at the trend over months, not days. Do not use it to judge your body or to chase a number.
Try it
Our waist-to-height ratio calculator works out your ratio in your browser. Nothing you enter is stored. To see your ratio next to your BMI, use the BMI and waist comparison.
Frequently asked questions
What is a good waist-to-height ratio?
The NHS says to try to keep your waist to less than half your height, which is a ratio below 0.5. It is not a diagnosis, and it does not apply to everyone (see the list of people who should not use it above).
Is waist-to-height ratio better than BMI?
It is not a replacement. The NHS describes it as a way to measure your health alongside BMI. The NIDDK notes that BMI does not directly measure body fat, so a waist measurement adds a second piece of information.
Can children use a waist-to-height calculator?
The NHS says its calculator is not for children under 5. For ages 5 to 17 it advises checking BMI first and using the calculator with a parent or carer. Our tools are written for adults, so please ask a healthcare professional about children.
How do I measure my waist?
The Public Health Agency in Northern Ireland describes measuring around your abdomen at roughly the halfway point between the bottom of your ribs and the top of your hips. Stand up straight, breathe out naturally and keep the tape snug. Measure the same way each time so you can compare results. A guide is also on the calculator page.
Does a ratio above 0.5 mean I have a health problem?
No. It is a screening measure, not a diagnosis, and the NHS says not to use its calculator to diagnose any condition. If you are worried about your waist size, contact your local pharmacist or GP surgery.
Sources
- NHS: Calculate your waist-to-height ratio
- NIDDK: Am I at a healthy weight?
- Public Health Agency (Northern Ireland): Are you inching towards bad health?
You may also be interested in:
- Why Your Waist May Grow as You Age
- Why Fiber Matters and Simple Ways to Eat More
- Does Walking Reduce Belly Fat? What the Guidelines Say
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This article is general education, not medical advice. Read our disclaimer and editorial policy.