Drywall guide
Drywall Formula Guide
Drywall is calculated by finding the total wall and ceiling area, subtracting openings, adding waste, and dividing by the coverage of one drywall sheet.
Calculate wall area from room perimeter and height, subtract doors and windows, add ceiling area if needed, then divide by sheet coverage.
Use the Drywall Calculator →Calculate Room Perimeter
Calculate Wall Area
Subtract Doors and Windows
Add Ceiling Area
If you are drywalling the ceiling, add the ceiling area to the wall area before applying waste.
Calculate Sheets Needed
Sheet coverage depends on the size of drywall panel you choose. A 4 × 8 sheet covers 32 square feet, a 4 × 10 sheet covers 40 square feet, and a 4 × 12 sheet covers 48 square feet.
Example Drywall Calculation
For a 20 ft by 15 ft room with 8 ft walls, the perimeter is 70 ft.
If you subtract one standard door and two windows, the drywall area is about 509 square feet.
With 10% waste, the adjusted area is about 560 square feet.
Using 4 × 8 sheets:
Round up to 18 sheets.
Common Drywall Calculation Mistakes
- Forgetting to include the ceiling
- Not subtracting doors and windows
- Forgetting to add waste
- Using the wrong sheet size
- Rounding down instead of rounding up
Frequently Asked Questions
What is the basic drywall formula?
Drywall area equals wall area plus ceiling area if needed, minus openings. Sheets needed equals adjusted area divided by sheet coverage.
How do I calculate drywall for ceilings?
Multiply room length by room width to get ceiling area, then add that to the wall area.
Do I need to include waste?
Yes. Most drywall projects should include 10–15% waste for cuts, mistakes, and damaged sheets.
Use the drywall calculator to estimate sheets, screws, tape, joint compound, waste, and cost.
Drywall Calculator →