Drywall Calculator

1. Choose your area mode. This drywall calculator supports two modes. Use "Room dimensions" if you know the room length, width, and wall height. Use "Known square footage" if you already calculated the total drywall area.
2. Enter room dimensions. Measure length, width, and floor-to-ceiling height in feet. Round up partial measurements. If your walls are 8 ft 6 in, enter 9 ft to avoid running short.
3. Include the ceiling if needed. Select "Yes" to add ceiling area to the wall total. Skip it if the ceiling is already finished or uses a different material.
4. Subtract door and window openings. Enter total square footage for doors and windows. A standard interior door is about 21 sq ft (3 ft × 7 ft). A typical window is about 15 sq ft (3 ft × 5 ft). Leave at 0 for a quick shopping estimate.
5. Pick your panel size. The most common residential size is 4 ft × 8 ft. Longer 4 ft × 12 ft sheets reduce seams on long walls but need two people to carry safely.
6. Set a waste factor. Use 10% for most rooms. Use 15% for small rooms, closets, or first-time projects where extra cuts and miscuts are more likely.

Pro tip: Compare 4 ft × 8 ft and 4 ft × 12 ft sheets in the panel comparison table below the drywall calculator results. Fewer seams means less taping and mudding, but longer panels are heavier and harder to handle alone.

The drywall calculator finds total wall and ceiling area, subtracts openings, adds waste, then divides by panel size to give you a sheet count.

Main formula:

Sheets needed = ceil(Adjusted area / Panel area)

Variables:

• Room length = straight wall measurement in feet
• Room width = perpendicular wall measurement in feet
• Wall height = floor-to-ceiling distance in feet
• Door/window area = square footage of openings to subtract
• Waste factor = extra percentage for cuts, damage, and layout losses
• Panel area = sheet width × sheet height (e.g., 4 × 8 = 32 sq ft)

Step by step:

Wall area:

Wall area (sq ft) = 2 × (Room length + Room width) × Wall height

Ceiling area (when included):

Ceiling area (sq ft) = Room length × Room width

Net and adjusted area:

Net area = Gross area - Door area - Window area

Adjusted area = Net area × (1 + Waste % / 100)

Example:

A 12 ft × 10 ft room with 8 ft walls, one door (21 sq ft), no ceiling, and 10% waste.

Finishing supply estimates:

• Joint compound: About 1 gallon per 100 sq ft of drywall. This covers three coats on standard butt and tapered joints.
• Joint tape: About 0.38 linear feet of tape per sq ft of drywall area. Paper tape is cheaper and stronger for flat joints. Mesh tape works better on patches and repairs.
• Drywall screws: About 32 screws per 100 sq ft when fastening to wood studs at 16 in OC. Use 1-1/4 in screws for standard 1/2 in panels.

Assumptions:

• The room is rectangular with straight walls. L-shaped or irregular rooms should be split into rectangles and calculated separately.
• Many installers skip door and window deductions on small rooms because the offcuts usually get used for patches, headers, and filler pieces above openings.
• Round up height measurements. If your walls are 8 ft 6 in, enter 9 ft. Using 8 ft leaves you short on panels cut to fit taller walls.
• Standard 1/2 in panels work for most walls. Use 5/8 in Type X (fire-rated) for garage ceilings, furnace rooms, and any assembly that requires a fire rating per local code. A 4 × 8 sheet of 1/2 in drywall costs $8 to $16 at most home centers (2026 prices).
• Use moisture-resistant (green board) or mold-resistant panels in bathrooms, laundry rooms, and basements. Standard drywall absorbs water and fails in high-humidity spaces.
• Buy 1 or 2 extra sheets as a safety margin. Damaged corners during delivery, miscuts around outlets, and crooked studs can all waste a panel you counted on using.

Quick rule for any drywall calculator estimate:

• A 4 ft × 8 ft sheet covers 32 sq ft
• A 4 ft × 12 ft sheet covers 48 sq ft but usually requires two people to hang
• Use 10% waste for most rooms, 15% for closets and complex layouts