Waist-to-Height Ratio vs BMI: What Each One Tells You
In short
BMI compares weight with height. Waist-to-height ratio shows fat around the middle. How to measure it, the NICE bands, and a worked example using both.
Waist-to-height ratio is your waist measurement divided by your height. The UK’s NICE guideline says to keep it under 0.5, which means keeping your waist to less than half your height. BMI tells you whether your weight is high for your height. Waist-to-height ratio tells you whether you carry extra fat around your middle. For adults with a BMI under 35, NICE recommends using both.
How to Measure Your Waist
NICE gives these steps:
- Find the landmarks. Locate the bottom of your ribs and the top of your hips.
- Wrap the tape midway between them. This is usually just above the belly button.
- Breathe out naturally, then take the measurement.
- Use the same units for height. Both in inches or both in centimeters. 5 ft 7 in is 67 inches.
- Divide waist by height.
Measure at the same spot each time. Moving the tape a couple of inches up or down is the most common reason the number changes from one check to the next.
The NICE Bands
| Waist-to-height ratio | NICE category | What NICE says it indicates |
|---|---|---|
| 0.4 to 0.49 | Healthy central adiposity | No increased health risks |
| 0.5 to 0.59 | Increased central adiposity | Increased health risks |
| 0.6 or more | High central adiposity | Further increased health risks |
NICE says these bands can be used for adults with a BMI under 35, of both sexes and all ethnicities, including adults with high muscle mass. The risks it names for higher central fat are type 2 diabetes, high blood pressure and cardiovascular disease. The bands were added in 2022 and are now part of NICE guideline NG246.
What BMI Does and Doesn’t Tell You
BMI is weight in kilograms divided by height in meters squared. NICE uses the familiar bands: 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight, and 30 or more is obesity. It calls BMI a practical measure but says to interpret it with caution, because it is not a direct measure of fat around the middle.
- Ethnicity. For people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean background, NICE uses lower thresholds, with overweight from 23 and obesity from 27.5, because cardiometabolic risk occurs at a lower BMI.
- Muscle. NICE says to interpret BMI with caution in adults with high muscle mass.
- Age 65 and over. NICE also advises caution here, noting that a slightly higher BMI may be protective in older age.
- A healthy BMI isn’t the whole story. NICE notes that a person in the healthy-weight range may still carry excess fat around the middle.
Why the Waist Adds Information
A 2012 meta-analysis of 31 studies, covering more than 300,000 adults in several ethnic groups, compared how well each measure picked out people with high blood pressure, type 2 diabetes, abnormal blood fats, metabolic syndrome and cardiovascular disease. Waist-to-height ratio did better than BMI, improving discrimination by 4 to 5%, and did better than waist size alone for several outcomes. That is a real but modest edge, and it describes screening accuracy, not a diagnosis.
Worked Example
5 ft 7 in, 150 lb, 35-inch Waist
| Measure | Arithmetic | Result |
|---|---|---|
| BMI | 150 lb = 68.04 kg; 67 in = 1.7018 m; 68.04 ÷ 1.7018² | 23.5, healthy weight on the standard bands |
| Waist-to-height ratio | 35 ÷ 67 | 0.52, increased central adiposity |
| Waist for a ratio of 0.5 | 67 × 0.5 | 33.5 in, so 1.5 in above that |
This person’s BMI looks fine on the standard scale, but the waist measure falls in NICE’s increased-risk band. If they were of South Asian background, for example, NICE’s lower thresholds would also put a BMI of 23.5 in the overweight range. Neither number is a diagnosis. Together they are a good reason to ask a doctor about blood pressure, blood sugar and cholesterol checks.
Limits of Both Measures
- Tape placement. Waist readings vary with where and how you measure, so compare like with like.
- BMI of 35 or more. NICE’s waist-to-height bands apply only below a BMI of 35.
- Children and teens. The adult bands don’t apply. NICE points to the NHS waist-to-height calculator for ages 5 and up.
- Pregnancy. Waist size during pregnancy doesn’t reflect body fat, so neither measure is useful then.
What This Doesn’t Cover
This guide compares two screening numbers. It doesn’t cover body fat percentage (see our body fat calculator), waist-to-hip ratio, or the blood tests a doctor uses to assess heart and diabetes risk. A doctor weighs these measures alongside blood pressure, blood tests, family history and medicines. If you have a history of an eating disorder, frequent body measuring may not help you, so talk with your clinician first. This page is for education only and is not medical advice.
Check Both Numbers
Enter your waist and height to see your ratio and NICE band, then check your BMI with the same height.
Sources: NICE guideline NG246, Identifying and assessing overweight, obesity and central adiposity (bands, measuring, BMI thresholds); Ashwell et al., 2012, Obesity Reviews (waist-to-height ratio vs BMI meta-analysis).
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