Free Diabetes & Metabolic Health Tool
Calculate your body mass index (BMI) and waist-to-height ratio, then use the explanations below to understand what these screening measures may—and may not— tell you about weight, abdominal fat, and cardiometabolic risk.
These results are screening measures only. They do not diagnose diabetes, insulin resistance, obesity-related disease, or cardiovascular disease.
BMI is calculated as weight in kilograms divided by height in meters squared. For adults, standard BMI categories are:
| Adult BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25.0–29.9 | Overweight |
| 30.0–34.9 | Obesity class 1 |
| 35.0–39.9 | Obesity class 2 |
| 40.0 or higher | Obesity class 3 |
BMI is useful because it is simple and widely studied, but it is not a direct measurement of body fat, muscle mass, or abdominal fat. A muscular person may have a higher BMI without having excessive body fat, while someone with a BMI in the healthy range may still carry more fat around the abdomen.
Waist-to-height ratio is calculated by dividing waist circumference by height using the same units. It is intended to give a practical estimate of central adiposity— fat carried around the abdomen.
| Waist-to-height ratio | NICE classification |
|---|---|
| 0.40–0.49 | Healthy central adiposity |
| 0.50–0.59 | Increased central adiposity / increased health risk |
| 0.60 or higher | High central adiposity / further increased health risk |
A simple way to remember the target is: try to keep your waist circumference to less than half your height. A waist-to-height ratio of 0.5 or above does not mean you already have diabetes or insulin resistance. It means central fat distribution may be adding to your overall cardiometabolic risk and may justify discussing other risk factors with your doctor.
Measurement technique matters. To measure your waist for waist-to-height ratio:
For example, a waist of 80 cm and height of 170 cm gives: 80 ÷ 170 = 0.47.
Excess body weight and central fat can be associated with insulin resistance, type 2 diabetes, high blood pressure, abnormal cholesterol, fatty liver disease, and cardiovascular disease. But these measurements are only part of the picture.
Blood pressure, family history, smoking, physical activity, sleep, medications, blood glucose, HbA1c, lipids, and other medical conditions can all change a person's overall risk.
BMI and waist size alone cannot diagnose diabetes. Use your overall risk profile and appropriate blood tests.
Use the Type 2 Diabetes Risk Calculator →A larger waist can be associated with metabolic risk, but it does not prove that you have insulin resistance.
What Is Insulin Resistance? →Learn how fasting glucose, HbA1c, OGTT, and home glucose readings differ.
Blood Tests for Diabetes →Sustainable food changes matter more than trying to achieve one perfect measurement.
Diabetes Food & Blood Sugar →Age can change body composition. Older adults may lose muscle while gaining fat, which can make BMI less informative when used alone. NICE advises interpreting BMI cautiously in adults aged 65 and over, taking health conditions, physical function, and the possible protective effect of a slightly higher BMI into account.
This does not mean there is one automatic “older adult BMI target.” Interpretation should be individualized, especially when frailty, unintentional weight loss, reduced muscle mass, or multiple medical conditions are present.
The BMI categories displayed by this calculator are intended for adults. BMI in children and teenagers needs age- and sex-specific interpretation rather than the fixed adult cutoffs above.
Waist-to-height ratio may also be used as an additional measure of central adiposity in children and young people aged 5 years and over, but it should be considered together with pediatric growth assessment rather than used alone.
They answer different questions. BMI is a practical measure of weight relative to height. Waist-to-height ratio focuses more specifically on central fat distribution. NICE recommends using waist-to-height ratio alongside BMI in adults with BMI below 35 kg/m² because the combination can add useful information about cardiometabolic risk.
It is better to think of these measures as complementary screening tools rather than competitors.
No. A high ratio can indicate increased central adiposity and higher cardiometabolic risk, but insulin resistance cannot be diagnosed from waist size alone.
Yes. BMI does not show where fat is stored, so some people with a BMI in the healthy range may still have increased central adiposity.
There is no need to measure it daily. If you are tracking lifestyle or weight changes, periodic measurements taken in the same way are more useful than frequent measurements that vary with technique.
Reducing excess central fat can be part of improving metabolic health, but risk also depends on glucose, blood pressure, lipids, family history, activity, medications, and other factors.