Drywall calculator

How It Is Calculated

This calculator estimates the number of drywall panels and the material cost for a rectangular room. The calculations follow these steps:

1. Wall area: The perimeter of the room is multiplied by the wall height.

   Wall area = 2 × (L + W) × H

   where L is room length, W is room width, and H is wall height.
2. Ceiling area: If the ceiling is included, its area is the floor area.

   Ceiling area = L × W

3. Total drywall area before waste: Sum of wall and ceiling areas.

   Total before waste = Wall area + Ceiling area

4. Apply waste factor: The waste factor F (as a percentage) is added to account for cuts and mistakes.

   Total area = Total before waste × (1 + F / 100)

   The result is rounded to the nearest whole square foot.
5. Panels needed: The total area is divided by the panel size S (32, 40, or 48 sq ft) and rounded up to the nearest whole panel.

   Panels needed = ⌈Total area / S⌉

6. Material cost: Multiply the number of panels by the price per panel P.

   Material cost = Panels needed × P

   The cost is rounded to two decimal places.

Assumptions

• Standard wall height is 8 ft.
• No deductions for doors, windows, or other openings; the waste factor accounts for these.
• Drywall panels are standard 4 ft width and 8, 10, or 12 ft length.
• Price per panel is for the drywall board only, not including tape, joint compound, screws, or labor.
• Waste factor typically 10–15% for drywall installation.

Worked Example

For a room with length = 12 ft, width = 10 ft, wall height = 8 ft, ceiling included, waste factor = 10%, panel size = 32 sq ft, and price per panel = $15:

1. Wall area = 2 × (12 + 10) × 8 = 2 × 22 × 8 = 352 sq ft.
2. Ceiling area = 12 × 10 = 120 sq ft.
3. Total before waste = 352 + 120 = 472 sq ft.
4. Total area = 472 × (1 + 10/100) = 472 × 1.10 = 519.2 → rounded to 519 sq ft.
5. Panels needed = ⌈519 / 32⌉ = ⌈16.21875⌉ = 17 panels.
6. Material cost = 17 × 15 = $255.00.

Results: Wall area = 352 sq ft, Ceiling area = 120 sq ft, Total drywall area = 519 sq ft, Panels needed = 17 panels, Drywall material cost = $255.

Practical Tips

• Measure the room carefully; even small errors can affect panel count.
• Order panels in full sheets; leftover pieces can be used for smaller areas.
• Consider the insulation calculator if you are insulating the walls before drywall.
• For a complete room finish, also check the paint calculator to estimate paint needed.
• If you are tiling a bathroom or kitchen, use the tile calculator for those surfaces.
• Always add a waste factor of 10–15% to cover cuts, mistakes, and future repairs.
• Drywall panels are heavy; plan for help with lifting and installation.