Standard numbers are 4 sq ft inside and 10 sq ft outside, per bird.
Before I knew that, we had raised 25 Cornish X Rocks in a 10x8 pen. They were in the basement in a brooder for two weeks, then six weeks out in the coop. The last couple weeks, they were pretty crowded... Space was lost to the two feeders and the waterer.
Most books say 10 square feet of outside room is enough. I think that is inadequate. 15 square feet of outside space or more is better for healthy birds. Also keeps you from having problems with fighting and canabalism.
So for 45 birds you need a run of at least 675 square feet.
Inside is recommended as 4-5 square feet per bird, but if you winters are bad then they will be spending more time inside then normal. In that case the inside needs to be increased.
If you try to stick with the standard sizes in books, you are going to have to clean the coop almost every day to keep the smell down. The more space you can give them the less smell and in alot of cases NO smell.