Body Mass Index (BMI) is weight (mass) in kilograms divided by the square of height in meters. I wrote this little applet in 2002 because the web forms back then were annoying. Adjust the vertical slider to your height and the horizontal slider to your weight.
|Green - normal:||[18.5, 25)|
|Yellow - overweight:||[25, 30)|
|Orange - obese:||[30, 40)|
|Red - extremely obese:||[40, ...)|
Note that these ranges are for adults. For kids see BMI For Children at the CDC.
For more information see BMI: Body Mass Index at the Centers for Disease Control.
But, beware. Wikipedia also says it is contoversial.