Calculating ideal weight and BMI
Body Mass Index (BMI), a measure of weight which takes account of height, was developed to enable people to compare ideal weights for those of different heights. The formula is weight in kg divided by the square of height in metres. But it's pretty hard to do this in your head (!), and gets even more complex if you are using imperial measurements (pounds, feet and inches). Luckily, there are various sites on the web which enable you to enter weight and height (in both metric and imperial) and calculate whether your BMI puts you in the underweight, normal or overweight range.
For example, the US National Heart Lung and Blood Institute has a simple and easy to use BMI calculator for adults.
Steven B Hall's site has a more complex set of various BMI calculators including information about where your weight falls in comparison to American men and women of the same age.
Interestingly, the different sites vary considerably in what they consider to be healthy BMI ranges for adults. Some say 20-25, some say 19-25 and others say 18.5-24. Few explain where these figures came from so it's difficult to establish which should be used. I've always been taught that 20-25 is appropriate but I'm not sure whether more recent research suggests a different range. There's also the issue of whether being in the 'normal' range means being average, or healthy. Steven Hall's site for example, tells me that a BMI of 25 is below average for American adults, although it's at the top of the 'healthy' normal range.
It's important to remember that using BMI for children (under 20s) is fraught with difficulties. For discussion of some of the issues around using BMI to define healthy weights for children see an article from the Children's Nutrition Research Center at Baylor College of Medicine and an another from the National Center for Chronic Disease Prevention and Health Promotion.
Keep Kids Healthy has a BMI calculator for children which takes account of age.
There's also Ian Frampton's 'weight for height' programme which calculates weight for height centiles for children and adolescents, but I couldn't find details of it on the web. If you're out there Ian, let me know details and I'll post them on the site.
Weight-for-Height: a computer based solution using Microsoft Excel spreadsheet solutions, which allow for accurate and fast calculation with instant graphical representations for an ongoing period. The programmes have already proved to be extremely useful in clinical settings where regular weekly updates on weight are an important factor in clinical decisions.