property clientHeight

This property returns the height of the visible document including padding. The margin, border and scroll bar values are not part of this width.

function DumpDimensions
{
    var box = scene.getBoxById("htmlBox");
    if (box)
    {
        shell.print("Client Width: " + box.clientWidth);
        shell.print("Client Height: " + box.clientHeight);
    }
}