How to use the drywall calculator
- Enter the room size and wall height. Use
12'or12' 6. - Choose whether to hang the ceiling.
- Count doors and windows. Each door subtracts 21 sq ft (3' × 7') and each window 15 sq ft. For big openings like a patio door, count it as two doors.
- Pick the sheet size. Longer sheets mean fewer butt joints but are heavier to hang.
The math
Wall area is the room's perimeter times the wall height. Add the ceiling (length × width), subtract openings, add waste and divide by the sheet area: 32 sq ft for a 4×8, 40 for a 4×10, 48 for a 4×12.
Example: a 12' × 12' room with 8' walls has 4 × 12 × 8 = 384 sq ft of wall plus a 144 sq ft ceiling. Subtract one door and one window (36 sq ft) for 492 sq ft of board. With 10% waste that's 541 sq ft ÷ 32 = 17 sheets of 4×8. It takes about 5 gallons of compound (two 4.5-gal pails), 182' of tape and roughly 490 screws.
Tips for fewer sheets and seams
- Hang ceilings first, then walls, with the top sheet tight to the ceiling.
- Run sheets horizontally on walls up to 8'1". Two 4' sheets cover the height with one taped seam at a comfortable working height.
- Use 4×12s on long walls and ceilings to cut down on butt joints, which are the hardest to finish flat.
- Fastening: follow the board maker and your code. Ceilings and fire-rated walls have tighter screw spacing.
Thickness
1/2" is standard for walls and most ceilings. 5/8" Type X is used for fire-rated walls and garage separations, and on ceilings with framing 24" O.C. Check local code for your situation.
FAQ
How many sheets of drywall do I need for a 12x12 room?
About 17 sheets of 4×8 for 8' walls and the ceiling, with one door, one window and 10% waste. Without the ceiling it's about 12.
How do I calculate drywall square footage?
Add up the room's wall lengths, multiply by the wall height, add the ceiling area (length × width), and subtract doors and windows. Divide by 32 for 4×8 sheets and add 10–15% for waste.
How much joint compound do I need?
USG lists about 10 gallons of ready-mixed all-purpose compound per 1,000 sq ft of board. A 4.5-gallon pail covers roughly 450 sq ft. Expect to use more for a smooth level 5 finish.
How many screws per sheet of drywall?
About 32 for a 4×8 sheet on walls with studs 16" O.C., or roughly one per square foot. Ceilings need closer spacing. Follow the board maker's schedule.