Billdr PRO Drywall Calculator

Our drywall calculator, also known as a sheetrock calculator, simplifies the process by helping you calculate the exact number of drywall sheets required. Whether you're covering walls or ceilings, this tool ensures that you purchase the right amount of drywall sheets, eliminating waste and saving you time and money. 

Calculating the number of drywall sheets you need for a room, including the ceiling and accounting for waste, involves a straightforward formula. 

Here are the steps to calculate it:

1. Measure the Room:

  • Measure the height of the walls from the floor to the ceiling.
  • Measure the length of each wall.
  • Measure the width of the room.

2. Calculate the Wall Area:

  • For each wall, multiply its height by its length to calculate the square footage of that wall.
  • Sum up the square footage of all the walls in the room.

3. Calculate the Ceiling Area:

  • Multiply the length by the width of the room to calculate the square footage of the ceiling.

4. Add Wall and Ceiling Areas:

  • Add the total wall area to the ceiling area to get the total square footage of the surfaces you need to cover with drywall.

5. Account for Waste:

  • It's common to add a waste buffer to account for cutting, mistakes, and unforeseen issues. A 10% buffer is a good starting point, but you can adjust it based on your experience and the complexity of the project. To add a 10% buffer, multiply the total square footage by 1.10.

6. Calculate the Total Drywall Area:

  • Multiply the total square footage (including the waste buffer) by 1.10 to get the total drywall area needed.

7. Determine Drywall Sheet Size:

  • Check the size of the drywall sheets you plan to use. Common sizes are 4'x8', 4'x10', and 4'x12'.

8. Calculate the Number of Sheets:

  • Divide the total drywall area (including the waste buffer) by the square footage of one drywall sheet. This will give you the number of sheets needed.


Number of Drywall Sheets = (Total Drywall Area with Buffer) / (Drywall Sheet Size)

Let's go through an example.

Suppose you have a room with:

  • Wall height: 8 feet
  • Four walls length: 12 feet, 12 feet, 10 feet, and 10 feet
  • Room width: 10 feet
  • Ceiling length: 12 feet
  • Ceiling width: 10 feet


  • Wall area = [(8 feet x 12 feet) + (8 feet x 12 feet) + (8 feet x 10 feet) + (8 feet x 10 feet)] = 288 sq. ft.
  • Ceiling area = 12 feet x 10 feet = 120 sq. ft.
  • Total wall and ceiling area = 288 sq. ft. + 120 sq. ft. = 408 sq. ft.
  • Adding a 10% waste buffer: 408 sq. ft. x 1.10 = 448.8 sq. ft.
  • If using 4'x8' sheets: 448.8 sq. ft. / (4 ft x 8 ft) = 14.025 sheets

Round up to the nearest whole number, so you would need 15 sheets of drywall to cover the walls and ceiling of this room taking into account a 10% waste buffer.

Looking for other tools?

Try one of our free Excel templates.

Build your business with the most valuable tool in your toolbox

Send $100K+ quotes in 30 minutes or less!

No credit card required

Contractor illustration