Inflated-layout calculator
Will the sleep setup fit the tent?
A tent's floor can be wide at the bathtub seam and much tighter where a thick pad and sleeping bag actually rise into the sloping wall.
Keep one real exit path
Do not fill the last inch on paper if somebody has to crawl across another sleeper, step on a pad, or pile wet gear against the wall to reach the door.
Pad sizing context: REI's sleeping-pad guide. The tent's measured floor, wall slope, and door path still come from the exact model and your setup.