steel tubing strenght formulas ??

Hi all,

I'm looking at 2 or 3" box tubing as a frame for a router.

It seems the stuff comes in different wall thickess and that would
offer different strenghts for vibration as well as flexing.

One of my concerns is a 5 foot lenght and how much it will bend under
cutting pressures.

Does anyone know how to calculate this ? or is there software that is
available ?

Dave