BMI and weight: what your numbers mean?

Body mass index (BMI) is one of the simplest ways to check whether your weight may be affecting your health. It takes a minute to work out, and it is usually the first measurement taken at a health screening. Here is what it tells you, what it doesn't, and when it is worth speaking to a doctor.

What is BMI?

BMI compares your weight with your height. It does not measure body fat directly, but across large groups of people it tracks closely with the risk of conditions such as type 2 diabetes, high blood pressure, high cholesterol and heart disease.

How to work out your BMI

Divide your weight in kilograms by your height in metres, squared:

BMI = weight (kg) ÷ height (m) ÷ height (m)

For example, someone who weighs 70 kg and is 1.65 m tall has a BMI of 70 ÷ 1.65 ÷ 1.65 = 25.7.

Or enter your numbers below to check yours:

What your BMI means for Asian adults

Research shows that Asian populations face higher health risks at lower BMIs than European populations. For this reason, Singapore uses lower cut-offs for adults:

• Below 18.5: risk of nutritional deficiency and some health problems
• 18.5 to 22.9: low risk
• 23.0 to 27.4: moderate risk
• 27.5 and above: high risk

These categories apply to adults. Children and teenagers are assessed differently, using growth charts for their age and sex.

Waist size matters too

Where you carry weight also matters. Fat around the waist is more closely linked to diabetes and heart disease than fat elsewhere. As a guide, health risks rise when waist circumference is:

• above 90 cm for men
• above 80 cm for women

Measure around your waist at the level of your belly button, standing relaxed and breathing out normally.

What BMI does not tell you

BMI is a useful starting point, but it is not a diagnosis. It does not distinguish between muscle and fat, so very muscular people can have a high BMI without excess fat. It also does not show where fat is stored, and it can be less accurate in older adults, during pregnancy and for people with certain medical conditions.

That is why doctors look at BMI together with your waist size, blood pressure, blood tests, medical history and lifestyle.

When to speak to a doctor

Consider a check-up if:

• your BMI is 23 or above, especially with a waist size above the guide
• you have gained weight steadily and find it hard to manage
• you have a family history of diabetes, high blood pressure or heart disease
• you have symptoms such as tiredness, loud snoring or breathlessness on exertion

A doctor can assess your overall health risk, arrange appropriate tests such as blood sugar and cholesterol, and talk you through a plan that suits your health and goals.

Medication for weight management

For some people, a doctor may suggest medication alongside changes to eating and activity. It is only prescribed after an assessment, and only if it is suitable for you.

This article is general health information and does not replace advice from your doctor.