BMI Calculator | Calculate Your BMI | Ramsay Health Care

BMI Calculator

BMI or body mass index is calculated using height and weight measurements to assess your body fat. Also known as the Quetelet index, the body mass index scale was developed by a Belgium statistician called Adolphe Quetelet in the 1800’s. Quetelet established this simple measurement for classifying peoples' weight relative to an ideal weight for their height.

Body mass index can be calculated using metric or imperial figures. It is defined as your body weight divided by the square of your height when using metric figures of kilograms and metres. It produces a unit of measure of kg/m². When using imperial pounds and inches the formula needs altering slightly to adjust it to the same BMI values as those calculated using metric units. This enables the universal use of a BMI score.

How to calculate BMI

Metric BMI formula
BMI = Weight (kg) / Height (m)²
The metric formula for BMI is weight in kilograms divided by height in meters squared. Often height is measured in centimetres. To convert your height to meters simply divide your height in centimetres by 100.

For example
If you’re height is 175cm and your weight is 75kg your BMI is calculated as follows:
75kg / (1.75m²) = 24.49kg/m²

Imperial BMI formula
BMI = [Weight (lbs) / Height (inches)²] x 703
The imperial formula requires you to divide your weight in pounds by your height in inches, squared. This figure is then multiplied by a conversion factor of 703.

For example
If you’re 5’5” (65 inches) in height and your weight is 150 pounds you BMI is calculated as follows:
[150lbs / (65 inches²)] x 703 = 24.96

BMI calculator

To make calculating your BMI easier, we have developed a BMI calculator. This tool allows you to simply enter your height and weight figures in either metric or imperial values and your BMI is computed for you.

You can bookmark this page if you’re monitoring your BMI maybe as part of a weight loss programme or just to keep abreast of your BMI and maintain a healthy BMI status.

What does your BMI value mean?

BMI is interpreted using standard weight status categories. These categories are the same for all adults, for both men and women, for all body types and they are age independent.

BMI weight categories

Below 18.5 - Underweight
18.5 to 24.9  - Normal or Healthy Weight
25.0 to 29.9 - Overweight
30.0 and Above - Obese

BMI of less than 18.5

If you’ve a BMI of less than 18.5 it would suggest that you’re underweight and you may need to put some on. Your doctor will be able to provide more advice.

BMI of 18.5 to 24.9

If your BMI is between 18.5 and 24.9 it suggests that you are a normal or healthy weight for your height. It’s obviously advisable to try and maintain this healthy weight and by doing so you may lower your risk of developing serious health conditions.

BMI of 25 to 29.9

If your BMI value is between 25 and 29.9 this indicates that you are overweight. It’s recommended that you talk to your doctor as they may advise you to lose some weight for health reasons.

BMI of 30 and above

A BMI of 30 or above is categorised as obese and indicates that you are heavily overweight. It’s recommended that you speak with your doctor as your health may be at risk if you do not lose weight.

Our BMI calculator details the BMI weight categories and their corresponding BMI scores and can be used as a useful reference point.


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