Post length vs. size of base plate?

[azcr2k]

For some reason I'm having issues today figuring out what size base plate to make for a post that has a 30lb wieght at 50" from the floor? Does anyone have a simple formula? I just want to post to not tip over without any outside forces acting on it. Thanks.

 

[Danger]

Welcome to PF, Azcr.
It's a bit more complicated than you indicate. If there were no forces at all acting upon it, you wouldn't need any plate.