Science -- Your Future, Scotland's Future
SCI-FUN Roadshow Exhibits -- Body Mass Index
SCI-FUN Roadshow Exhibits -- Body Mass Index
In this exhibit you learn about being a healthy weight for your height and age.

Measuring BMI is one of the ways we can see how healthy a person is. BMI compares your weight to your height to see how healthy you are.

You can calculate your BMI by this equation:

BMI = weight (kg) / height (m)2

Once you know your BMI, you can see if it's healthy for your age by comparing it to known ranges. The range of a healthy BMI changes with age, because of your changing body shape. For example, an adult is considered underweight if their BMI is under 18.5, but an 11-year-old girl can have a BMI as low as 14.5 and still be healthy, because at this age she will be growing a lot in height, but not putting on as much weight.

BMI can give an estimate of how healthy your weight is, but it is not always accurate. Because muscle is heavier than fat, athletic people (lots of muscle and very little fat) often find that their BMI indicates them to be overweight, even though they are actually healthier than most people.

There are other methods of calculating how healthy someone's weight is. Measuring body fat percentage is a very accurate measure of health, however it requires specialist equipment. Women should have around 8-12% body fat, and men around 3-5%, in order to be healthy. Health can be more easily estimated from your waist-to-height ratio (under 0.5 is healthy under age 40). This estimate is thought to be more accurate than BMI, but still not as accurate as body fat percentage.

Maintaining a healthy weight is important for your long-term health. The best way to be a healthy weight is to eat a balanced diet with lots of fruit and veg and take plenty of exercise. If you are concerned about your weight, if you think you might be overweight or underweight, speak to your doctor about how to lose or gain weight in a healthy way.

1 Measuring BMI is a way to see how ________ a person is.
2 Use the BMI equation to calculate your BMI.
3 Why does the healthy BMI range change with age?
4 Why is BMI an inaccurate measure of health in athletes?
5 What percentage body fat is ideal for a woman?
6 Why do you think that women need more body fat than men?

1 Look in gossip magazines for celebrities labelled as "too fat" or "too thin". Look on the Internet to find out height and weight then calculate their BMI. Are they healthy weights for their heights? Do you think the magazines have been fair?
2 Keep a food diary for a week for you and your family. How healthy do you think your diet is? Are all the food groups represented? Do you think there's anything you eat too much or too little of? Can you think of any way that you could change your diet to make it healthier?