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Body Mass Index Calculator

The Body Mass Index (BMI) is a way of estimating how thin or obese you are and how much fat your are carrying based on your weight and height. On this page there is a calculator for weight in kilograms and height in metres and a calculator for weight in stones and pounds and height in feet and inches (go to Imperial Calculator). The basic interpretation of BMI given below the metric calculator is for adults only, for children a more complex interpretation should be used.

BMI Calculator - Metric

To use our metric BMI calculator enter your weight in kilograms in the Weight box, you can use decimal notation. Then enter your height in metres into the height box, if you are 1m 70cm tall enter 1.70 as your height. Your BMI will then appear in the BMI box.

Weight (kg)   Height (m) BMI
kg m =

Understanding Your Body Mass Index Value

For adult men and women BMI values can be interpreted as per the following rules:

  • < 18.5 - Underweight
  • 18.5 - 24.9 - Normal Weight
  • 25.0 - 29.9 - Over Weight
  • > 30.0 - Obese

If you are concerned about your weight and especially if your BMI is greater than 30 you should consult your doctor or a health professional who will be able to advise you as to an appropriate course of action.

For those of you looking for calorie counts we are working with howmanycaloriesin.info to provide extensive lists in metric units.

BMI Calculator - Imperial

To use our Imperial BMI calculator enter your weight in stones and pounds into the Weight boxes (alternatively for US weight formats you can just enter your weight in pounds into the pounds box). Then enter your height in feet and inches into the height boxes.

Weight (st & lb) Height (ft & in) BMI
st lb ft in =

Weaknesses Of Body Mass Index Calculation

BMI measurements for taller people are generally slightly higher than those for shorter people, this is due to the calculation using height squared in the denominator of the formula. If all dimensions of the body were doubled to maintain a steady index then height cubed should be used in the calculations - this measurement is known as the Ponderal index.

However the Ponderal index also has weaknesses as the bodily dimensions of someone 2m tall are not all double those of someone 1m tall. Taller people tend to have narrower frames, in relation to height, than shorter people. Theoreticians have postulated that the ideal index would be to take an exponent of between 2.3 and 2.7 of height - this lies somewhere between height squared and height cubed.