Calculate your BMI

What is BMI?

Body mass index (BMI) is a health metric used to gauge a person's weight category quickly, as it is a simple calculation of body fat relative to weight and height. While BMI has its limitations - and should not be the only metric considered when determining your weight class - it is a fast and accessible tool that can help you better understand whether you carry excess body fat, which can put you at risk for health complications ranging from type 2 diabetes to high blood pressure.

BMI CALCULATOR

Measurement System:
Weight (Kg):
Height (Cm):

How to use the BMI calculator

  • Using the metric system, the BMI calculation divides an adult's weight in kilograms (kg) by their height in metres (m) squared.

    For example, if you weigh 70kg and are 1.73m tall, you work out your BMI by:

    Squaring your height: 1.73x1.73 = 2.99
    Dividing 70 by 2.99 = 23.41

    Your result will be displayed to 1 decimal place, for example 23.4.
  • BMI is calculated by dividing your weight in pounds by the square of your height in inches, and then multiplying by a conversion factor of 703. See the formula below for an example:

    Weight = 150 pounds
    Height = 5’5″ (65 inches)
    BMI calculation: [150 ÷ (65)^2] x 703 = 24.96

BMI chart for adults

BMI chart
A BMI calculation in the healthy weight range is between 18.5 to 24.9.

For Black, Asian and some other minority ethnic groups, the healthy weight range is 18.5 to 23.

For people of White heritage, a BMI:
  • below 18.5 is underweight
  • between 18.5 and 24.9 is healthy
  • between 25 and 29.9 is overweight
  • of 30 or over is obese
Black, Asian and some other minority ethnic groups have a higher risk of developing some long-term conditions such as type 2 diabetes with a lower BMI. People from these groups with a BMI of:
  • 23 or more are at increased risk (overweight)
  • 27.5 or more are at high risk (obese)

Frequently Asked Questions(FAQ)

BMI can be a screening tool, but it does not diagnose the body fatness or health of an individual. To determine if BMI is a health risk, a healthcare provider performs further assessments. Such assessments include skinfold thickness measurements, evaluations of diet, physical activity, and family history.

A healthy BMI for adults ages 20 and up is between 18.5 and 24.9, according to the NHS. Keep in mind, though, the limitations outlined in this article, and talk to your doctor about any weight-related concerns.

Your BMI, or Body Mass Index, is a measure of your weight compared to your height. Accurate assessments of obesity are important, as being overweight or obese significantly increases your risk of a variety of medical conditions including type 2 diabetes, heart disease and cancer. As levels of overweight or obesity increase, the spotlight has fallen on BMI and its shortcomings as a measure of ideal weight for individuals, rather than whole populations of people where "averages" apply.

For most adults, BMI gives a good estimate of your weight-related health risks. If your BMI is over 35, your weight is definitely putting your health at risk, regardless of the factors below. However, there are some situations where BMI may underestimate or overestimate these risks in the 25-35 BMI range. The main ones are:
  • Children - Your GP or health visitor can advise on where your child sits on the "centile charts" used to estimate healthy weights for children.
  • Pregnant women - Usual BMI estimates do not apply if you are pregnant.
  • Very muscular people - BMI assumes you have an average amount of body fat, including "intra-abdominal fat" - fat deep inside your stomach cavity rather than under your skin. Intra-abdominal fat is much more closely linked to risks of type 2 diabetes and heart disease than fat under the skin.

    If you are very muscular, your level of body fat may be lower than predicted by your BMI. However, this only applies to people who do high levels of exercise - much more than average.
  • People of Asian origin - People of Asian origin are prone to accumulating intra-abdominal fat (fat deep inside your stomach cavity rather than under your skin) at a lower BMI than people of Caucasian origin. People with this pattern of weight gain are described as "apples" rather than "pears" from their body outline. This means their health risks start to rise at a lower BMI, because intra-abdominal fat is directly linked to development of heart disease and type 2 diabetes.

    The World Health Organisation has looked at the evidence and because of the variability between different Asian populations, it hasn't officially changed the cut-off points. However, it does recommend that for public health purposes, some Asian groups should be considered overweight if their BMI is 22-25, and obese with a BMI of 26-31.
  • Older people (over 65, possibly over 60) - Because muscle mass tends to drop and body fat tends to rise in older people, BMI may not be an accurate reflector of body fat if you're over 60.

For people who are overweight (a BMI of 25.0 or higher) or living with obesity (a BMI of 30.0 or higher), potential health risks include high blood pressure, high LDL or low HDL cholesterol, type 2 diabetes, heart disease, stroke, gallbladder disease, sleep apnea and more. Those who are overweight or living with obesity may also have an increased risk of mental illness including clinical depression and anxiety.

People who are underweight (whether from an underlying medical condition or from poor diet) may be at risk for deficiencies that could lead to osteoporosis and anemia.

People who are underweight may also have a weakened immune system, which could make them more likely to contract the flu, a cold or other infection. Women who are underweight may experience cycle and fertility issues.