Work out how many drywall sheets, plus roughly how much joint compound and screws, you'll need for a room's walls and/or ceiling.
4×8 ft sheets are easiest to handle and most common for DIY; 4×12 ft sheets cover more area with fewer seams, which pros often prefer for large walls.
As a rough guide, budget one standard box (~12.5 kg) of pre-mixed joint compound per 500 sq ft of drywall, more if you're doing a Level 5 smooth finish.
Yes if you're drywalling it — just enter the ceiling's square footage in the optional 'Ceiling Area' field and it will be added to the total.