Will two sheets do?

[davsas]

I am replacing the chipboard in the bathroom with 3/4 marine ply. The sheets measure 1200mmx 2440mm, the bathroom is 3180 x 1820 mm, I'm thinking 3 sheets, two fitted whole and the other to fill the spaces?

 

[Jackrae]

Properly cut, here is only one space - but it all depends on where the joists are. Or why not leave the chipboard down and cover with the marine ply; that way all joints are supported.

Cut the sheets to 1200 x 1820 then either fit 2 at 1200 plus 1 at 700 or cut all three to 1060 and you have the sheets evenly spaced.

 

[davsas]

The current floor got soaked when the shower leaked and has gone to mush, also I redoing the pipe work so need to lift it anyway.
The joists run the length, so the 3180, and are 400 apart