How Much to Buy

Drywall calculator

Enter the room size, openings and sheet length. Get the number of sheets for walls and ceiling.

Room size
ft
ft
ft
Openings and extras
Sheets
%
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What to buy

Enter your measurements to see how much to buy.

How the drywall math works

Walls: 2 × (length + width) × height − openings
Ceiling: length × width
Sheets = total × (1 + waste %) ÷ sheet area (rounded up)

Worked example

A 12 × 12 ft room with 8 ft walls, one door and one window has 348 sq ft of wall plus a 144 sq ft ceiling: 492 sq ft. With 10% waste that’s 541 sq ft, or 17 sheets of 4 × 8 or 12 sheets of 4 × 12.

Which sheet length?

Longer sheets mean fewer joints to tape and finish, which saves time and joint compound. They are also much heavier and harder to get through doors and up stairs. 4 × 8 is easiest to handle alone; 4 × 12 usually needs two people.

Check before you buy: this is an area-based estimate. Pros often lay out each wall to minimize joints, which can change the count by a sheet or two. Fire-rated, moisture-resistant and ceiling-specific boards may be required in garages, bathrooms and some ceilings by local code.

Common questions

How many sheets of drywall for a 12×12 room?

With 8 ft walls, a ceiling, one door and one window: about 17 sheets of 4 × 8 or 12 sheets of 4 × 12, including 10% waste.

Should I subtract doors and windows?

This calculator does, using 21 sq ft per door and 15 sq ft per window. Many pros skip subtracting small windows because the offcuts are rarely usable; raising the waste allowance has a similar effect.

How much waste should I plan for?

10% is common for simple rooms. Rooms with many angles, soffits or small wall sections may need 15%.

What thickness of drywall do I need?

1/2 inch is standard for most interior walls. 5/8 inch is common for ceilings with wider framing and where fire-rated board is required. Check local code.

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