http://www.genesis-rc.com/wacoymf5/wing%20loading.htm
http://members.dca.net/mcquaide/Aerobatics/tools.htm

Here are a couple of site that may better explain wing loading.

At home I have a nice cubic calculator that I can't find here at work.
I tend to use cubic for the 33~40% as it's a better indicator for me_bob