On Nov 11, 7:42 pm, pollyfan wrote:
No wall under the proposed space. The joists are 2x9, and where the
bath will go they are (oddly) 4", 12", 13", and 4" apart! Also the
floorboards above them are set diagonally across them--don't know if
that spreads the load any differently.

The span of the joists also enter into this.

Google "floor joist load calculator' for some additional information.