Drywall Calculator

Calculate the number of drywall sheets for walls and ceilings — choose sheet size, deduct doors and windows, and get an optional cost estimate.

Room details

ft
ft
ft
Each deducts 20 ft² (1.86 m²).
Each deducts 15 ft² (1.39 m²).
%
8 % is standard for drywall cut losses.
$

Calculation results

Sheets needed

— sheets

Net area

— ft²

Total surface area

— ft²

Sheet count rounded up. Don’t forget to budget for joint compound (mud), tape, screws and corner bead — typically $15–25 in consumables per sheet installed.

Informational only. These are material estimates. Drywall installation requires proper fastening, taping and finishing — consult a licensed contractor for fire-rated assemblies, moisture areas and structural applications.

Understanding the formula

Total surface area minus door and window deductions gives the net paintable area. The waste factor accounts for cut loss, then the result divides by sheet area.

walls = 2 × (L + W) × H  ·  net = walls + ceiling − deductions  ·  sheets = ⌈ net × (1 + waste) / sheet area ⌉

A 4 × 8 ft sheet covers 32 ft². A 4 × 10 ft sheet covers 40 ft² and is often preferred for 9-ft ceilings, since it avoids a horizontal seam that would fall at eye level.

Worked example

A 12 × 10 ft room at 9 ft, ceiling included, 1 door, 1 window, 4×8 sheets, 8 % waste:

  • Walls = 2 × (12 + 10) × 9 = 396 ft²
  • Ceiling = 12 × 10 = 120 ft²
  • Deductions = 20 + 15 = 35 ft²
  • Net = 396 + 120 − 35 = 481 ft²
  • Sheets = ⌈ 481 × 1.08 / 32 ⌉ = ⌈ 519.5 / 32 ⌉ = ⌈ 16.2 ⌉ = 17 sheets

Common mistakes & tips

  • Match sheet height to ceiling height. A 4 × 8 sheet leaves a horizontal seam at 8 ft, which requires finishing. For 9-ft ceilings, use 4 × 9 sheets to run the full height. For 10-ft ceilings, use 4 × 10 or run two rows of 4 × 8.
  • Install ceiling drywall first. Ceiling sheets go up before wall sheets — wall boards butt against the ceiling and help support the ceiling edge.
  • Stagger seams. Offset vertical seams between rows by at least 16 in (one stud spacing) to avoid a straight crack running floor to ceiling.
  • Use the right thickness. 1/2 in is standard for walls and ceilings. 5/8 in is required for garage ceilings below living space (fire rating). 3/8 in is used for curved surfaces only.
  • Budget for three coats of mud. A professional drywall finish requires three coats of joint compound, each fully dried and lightly sanded between coats.

Frequently asked questions

How many sheets of drywall for a 12 × 12 room?
A 12 × 12 ft room at 8 ft ceiling has 384 ft² of wall area. With one door and one window deducted (35 ft²), net = 349 ft². At 8 % waste, sheets = ⌈349 × 1.08 / 32⌉ = 12 sheets of 4×8. Including the ceiling adds 4 more sheets.
Should I use 4×8 or 4×12 drywall?
4×8 sheets are easiest to handle and available everywhere. 4×12 sheets create fewer seams (one horizontal seam instead of two for a 9-ft wall) but are heavy and harder to manoeuvre. Professional crews use 4×12 for efficiency; DIYers usually stick with 4×8.
What thickness drywall for walls?
1/2 inch (12.7 mm) is standard for residential walls and ceilings. Use 5/8 inch for fire-rated assemblies (garage ceiling, stairwell walls). 3/8 inch is only for second-layer repairs or tight curves.
How much joint compound (mud) do I need?
A rule of thumb is about 0.053 gallons of pre-mixed compound per square foot of drywall. A standard 4.5-gallon pail covers roughly 85 ft² for all three coats. Buy one pail per 5–6 sheets as a starting estimate.
How do I drywall around a door?
The calculator deducts the door area from the wall. In practice, run full sheets over the opening, then cut out the door rough opening with a router or saw after the sheet is fastened. This reduces seams and waste.
What is the waste factor for drywall?
The industry standard is 8 %, which accounts for cuts around outlets, windows, doors, corners and seam offsets. Complex rooms with many angles or partial walls may need 10–12 %.