You can look up or use one of the calculators to get the section
modulous for the various angles and tubes you would consider. Typically,
a tube shape has more strength in both directions than a rectangular
tube of the same weight per foot.

But a word of warning: tube and angle fail in different modes, you
really can't just sub one for the other without a bit of care. That
said, 2x3x1/4 angle is fairly wimpy stuff if used as frame rails.

Edward A. Falk wrote:
Hi all; about to start building a trailer. The trailer plans I
bought from trailerplans.com call for 2"x3"x1/4" angle iron. I
want to use steel tube instead. Can anybody give me an idea of what
size steel tube would have the same strength? Is there somewhere
this can be looked up?