This is the home page for TopCode's BMI widget.
There are many BMI widgets around. The BMI calculation is a simple formula:
BMI = weight x height squared
What makes this calculator different is that its multi-national - users can choose whatever system of units they are familiar with.
For the technically minded, the widget is written in PHP. All the frames reside in one file. The "form action" is to call itself, but different paths are taken depending on the previous action.