How much drywall do you need?

Add up your total wall and ceiling area in square feet, add a waste factor (10–15%), then divide by the coverage of your sheet size and round up. A 4×8 sheet covers 32 square feet, a 4×12 covers 48. So 1,000 square feet at 10% waste with 4×8 sheets is about 35 sheets.

4×8 sheets are easiest to handle solo and fit through tight spaces. 4×12 sheets cover more area with fewer seams — less taping and a cleaner finish — but they're heavy and need two people. Pros often use 4×12 on long walls and ceilings to cut down on butt joints.

A rough rule is about one box or bucket of compound per 400–500 square feet, and roughly the same linear footage of tape as your total seams. These swing a lot with finish level and technique, so treat the numbers here as a starting estimate and buy a little extra.

Plan on roughly 32 to 40 screws per sheet depending on whether it's wall or ceiling and your fastener spacing — very roughly about one screw per square foot. A pound of drywall screws is several hundred screws, so most rooms need only a few pounds.

For a quick estimate, no — leaving openings in the total gives you built-in waste for cuts and mistakes. On a big job with large openings you can subtract them, but then keep your waste factor at 15% to stay safe.