Understanding your healthy weight: Body mass index (BMI) and waist circumference

Maintaining a healthy body weight has a number of positive benefits and can make an impact on your overall health.

Understanding your healthy weight

It's important to have an idea of your body mass index (BMI) and your waist circumference. These measurements are just a rough guide but can be beneficial in establishing what our ideal weight range may be.

Body mass index (BMI)

The BMI scale uses both your weight and height in order to work out if your weight is in a healthy range.

To calculate your BMI, you'll need to:

  1. find your weight in kilograms (kg) and the square of your height in metres
  2. divide your weight by your height

Your BMI will fit into one of 4 categories:

  • underweight - those with a BMI of under 18.5
  • healthy weight - those with a BMI between 18.5 and 24.9
  • overweight - those with a BMI between 25 and 29.9
  • obese - those with a BMI between 30 and 39.9
  • morbidly obese - those with a BMI of 40 or over
BMI chart
Use our chart to find out if you are over or under weight using your BMI result NHS inform

It's important to remember that BMI isn't a suitable measurement for certain people, including:

  • children - there  is a separate BMI chart for monitoring BMI in children, ask your health visitor or GP if you would like more information on this
  • pregnant women
  • athletes or those who're extremely muscular

BMI calculations don't take into consideration your body composition (e.g muscle, fat, bone density), sex and other factors which can impact your weight. However, it's a useful and quick way to indicate if you're in a healthy weight range.

Waist circumference

Waist circumference is a measurement used by doctors and dietitians to determine if you're overweight, and if that excess weight is putting your health at risk.

Measuring your waist is a good way to check you're not carrying too much fat around your stomach, hips and buttocks. If you store most of your weight around your midsection (over your hips and thighs) then you could be at an increased risk of type 2 diabetes.

You can have a healthy BMI and still have excess tummy fat – meaning you're still at risk of developing type 2 diabetes.

A healthy waist circumference is:

  • 80cm (31.5in) for all women
  • 94cm (37in) for most men
  • 90cm (35in) for South Asian men

How to calculate your waist circumference

You can calculate your waist circumference by yourself with a tape measure.

To measure your waist:

  • stand up straight and breathe out naturally before taking the measurement
  • wrap a tape measure around the smallest part of your waist and take the measurement - this is your waist circumference

If you're not sure you're a healthy weight, your doctor will be happy to carry out the measurement for you and advise you on the results.

Why a healthy weight range is important

Maintaining your BMI and waist circumference within the healthy range may protect you from developing potential health problems.

Health problems associated with a BMI in the obesity range include:

  • type 2 diabetes
  • stroke
  • heart disease
  • some cancers
  • issues with fertility in women
  • high blood pressure
  • osteoarthritis
  • fatty liver disease
  • kidney disease

Health problems associated with being underweight include:

  • weakened immune system
  • osteoporosis
  • anaemia
  • issues with fertility in women
  • palpitations