I'm sure you've heard of BMI or Body Mass Index but have you ever wondered how it is actually worked out? It really isn't that a complicated formula and if you have ever used Wii Fit or an online BMI calculator then you will know that you put in both your weight and height for the computer to give you a BMI figure. The online calculator or Wii Fit will then tell you whether you fit within the healthy weight range, are underweight or whether you are overweight. That is the great benefit of computers – they do all the calculating for you, you just enter a couple of numbers and it gives you the result. But getting an instant answer doesn't let you know how it's worked out and what it all means. So let's first take a look at what BMI is and how the BMI number is calculated.
BMi measures body mass by comparing your height and weight. It divides your weight by your height squared and you are then left with a single number. It will depend on where that number falls on the chart as to whether you are underweight, in a healthy weight range or overweight.
BMI calculations can often be inaccurate because of the fact that it doesn't measure body fat. For athletes, football players and anyone that has a lot of muscle, they will get an inaccurate result. Muscle actually weighs more than fat and the BMI formula doesn't take this into account. But if you are an average person with an average amount of muscle and body fat, then the BMI formula will be quite accurate.
How is BMI calculated?
The basic formula for calculating BMI is kg/m2. This is your weight (in kilograms) – divided by your height (in meters), squared. So for example, if a person is 1.7 meters tall then you would square that number (times it by itself) which is 1.7 times 1.7 which equals 2.89. Next you divide the persons weight, so if that person weighed 68 kilograms you would divide 68 by 2.89 which equals 23.5.
A healthy weight range is between 18.5 and 24.9 so if your BMI results is lower than 18.5 then this indicates that you are underweight. If you fall between the range of 18.5 and 24.9 then you have a healthy weight. If your BMI results i between 25 and 29.9 then this indicates that you are overweight. If your BMI result is over 30 then this indicates that you are obese.
If you work in pounds and feet rather than kilograms and meters then you can just change the formula to suit. You would
then multiply the weight of 150 pounds, times 4.88 which equals 732. Then divide the height of 5.5 feet squared, which is 30.25. So it would be 732 divided by 30.25 which equals 24.1. This is a slightly higher result than the metric result but not too much.