I'm mathematically challenged.
Here's what I did:
I had the grids, put them together like a side would be, all in a line, and then held it up to the space I had to put it in, and figured out how many would fit.
My cage is 2x4 in grids. The exact measurements of the OUTSIDE perimeter... are 29" x 58". The interior space of the 2 grids is equal to approx. 27".
I hope that helps a little bit...