BMI Calculator

BMI (body mass index) is a measurement of your healthy weightfor your height. Use this BMI calculator to measure the adults in your family.

For children, go to Weight Concern's Child and Young the body mass index (BMI) tool. Imperial

The calculator should only be only used to measure the weight of adults (pregnant or lactating mothers should not be relying on the BMI readings) and no decision should be decided based upon its findings aside from consulting a suitably qualified person such as a physician.

The calculator can give you an some idea of how your weight is compared to the norm for values. Body Mass Index (or BMI) is calculated as you weight (in kilograms) divided by the square of your height (in metres) or BMI = Kg/M2.

Is Body Mass Index reliable?

Your BMI is also known as Body Mass Index, is the measure of your weight in relation to your height. The accuracy of your assessment of obesity is crucial, since being obese or overweight significantly increases your risk for a range of health conditions, including type 2 diabetes, heart disease and cancer. With the rate of weight gain or obesity increase the spotlight has been placed onto BMI and its weaknesses as a measure for ideal weight for an individual, rather than whole populations of people for whom "averages" apply.

"Some people naturally have a larger frame than others. But this causes quite a small variation in weight and is accounted for in the range of healthy BMI. There is really no such thing as someone who is big-boned. " Dr Jan Sambrook, How to lose weight in a healthy way

For most adults BMI provides a reliable estimate of your weight-related health risk. If your BMI is over 35, your weight is most likely to put your health at risk regardless of the variables below. But, there are circumstances in which BMI may underestimate or overestimate those risks for the 25-35 BMI range. The most prevalent are:

Children

Your GP or health visitor can help you determine where your child sits on the 'centile charts' that are used to determine the weights that are healthy for children.

Pregnant women

Usual BMI estimates do not apply if you're pregnant.

If you're extremely muscular

BMI assumes you've some body fat, which includes 'intra-abdominal fat', an abdominal fat that lies deep within your cavity rather than under your skin. Intra-abdominal fat is more closely linked with risk of type 2 heart disease and diabetes than fat that is under the skin.

If you're a very strong person, your level of body fat may be lower than expected by your BMI. However, this only applies to those who engage in high levels of exercise - much more than average.

If you're of Asian or Asian descent, you're in the right place.

People who are of Asian origin are more likely to develop abdominal fat (fat deep inside your stomach cavity , rather than beneath your skin) with lower BMI levels than those who are of Caucasian origin. People who suffer from this pattern with weight gains are described as 'apples' , rather than "pears" from their outline. This implies that their health risks increase with a lower BMI since abdominal fat is directly associated with development of heart disease and Type 2 Diabetes.

The World Health Organisation has looked at the evidence and , because of the varying characteristics between Asian populations, it hasn't officially changed the cut-offs. However, the WHO recommends that , for the sake of public health certain Asian groups should be considered overweight if their BMI is 22-25 or obese with an BMI between 26-31.

People who are older (over 65, possibly 60)

Because muscle mass tends decrease and body fat tends to increase in older individuals The BMI might not be an accurate measure of body fat when you're older than 60.

Alternative estimates of health-related weight risks

If you feel BMI may not accurately tell you if you're overweight or obese, measuring your abdominal circumference, waist, or waist ratio may give you a more realistic estimate.

Waist circumference

The waist circumference is measured about halfway between the bottom of your ribcage to at the highest point of the hip bone using a tape measure that is in line with the floor. It is essential to breathe out while you take measurements. Male

• Risk of increased health - >=94cm
• High risk of health - > 102cm

Female

• Risk of increased health - >80cm
• Health risks for the elderly >= 88cm

Ratio hip-to-waist

To assess your waist-to- hip ratio, measure your waist circumference (as above) as well as your hip size at the broadest point of your hips. Divide your abdominal circumference by your hip measurement to give an approximate ratio.

• For women, a waist-to- hip ratio higher than 0.85 is associated with greater than average risk.
• For men with a waist to hip ratio of more than 1.00 is associated with a higher than the average risk.

The ratio of height to waist

A recent study that compared BMI along with waist circumference, hip-to-waist ratio, and the ratio of waist to height discovered that the most accurate way of predicting your total body fat percentage was to look at the waist-height ratio.

The waist circumference should be measured as above, and then divide it by your height - clearly both measurements must or be either in imperial (inches) or the metric (cm).

Whole body obesity is defined by a waist-height ratio of:

• 0.53 or higher for males
• 0.54 plus for females

Abdominal weight gain is measured by a waist-to-height proportion of 0.59 or more.

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