Probably. You should take actual dimensions from the toilet if possible, and/or make sure you can return it if the dimensions don't work. I have found that the actual toilet can vary from what the specs show. One other thing to be aware of is that the base may be closer to the wall than the back of the tank, and any molding at floor level will further reduce the clearance you think you have.

Thanks. We also have the issue of the door opening into the toilet so we need one that's not too deep also. I'm making my husband nuts--everything he likes is really big.

These can be tricky; we did one years ago. Kudzu is right that the dimensions can vary slightly.

You do not say if the sheetrock is already in place or if you are down to the studs. Remember that the sheetrock takes some space too. The pipes are hopefully the correct depth into the wall.