An interactive applet and associated web page that demonstrate the area of a square. The applet shows a square with all vertices draggable. As you drag any one, the area id continuously calculated and shown on the applet. The square is filled with a unit grid to allow class estimation of area. The displayed calculation can be turned off.

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.