How Much Drywall Do I Need?

Whether you're finishing a basement, renovating a bedroom, or building new construction, ordering the right amount of drywall saves money and prevents mid-project delays. Too little means an extra trip to the store (and possible lot number mismatches). Too much means wasted material and money. This guide walks you through exactly how to calculate drywall quantities for any project.

The Basic Drywall Formula

The core formula for calculating drywall is simple:

Total Area (sq ft) = Wall Height x Wall Width
Net Area = Total Area - Door/Window Openings
Sheets Needed = Net Area x (1 + Waste%) / Sheet Size (sq ft)

For a rectangular room, calculate all four walls: Total Wall Area = 2 x (Length + Width) x Height. This gives you the gross wall area before any deductions.

The most common mistake is forgetting to add a waste factor. Drywall must be cut to fit around electrical outlets, light switches, corners, and odd angles. These cuts generate scrap pieces that usually can't be reused. A 10% waste factor handles most standard rooms; use 15% for rooms with many openings or complex layouts.

Step-by-Step Calculation Process

Step 1: Measure Each Wall

Using a tape measure, record the width and height of every wall surface that will receive drywall. For rectangular rooms, you only need the room length, width, and ceiling height -- the formula calculates all four walls automatically.

Pro tip: Don't assume all walls are the same height. Older homes often have slight variations. Measure each wall individually and use the tallest measurement for ordering purposes.

Step 2: Count Doors and Windows

Standard door openings are approximately 3 feet wide by 7 feet tall (21 sq ft). Standard windows are approximately 3 feet wide by 4 feet tall (12 sq ft). Count every door and window in the room and multiply by these standard sizes. For non-standard openings (sliding glass doors, picture windows, archways), measure the actual width and height.

Step 3: Calculate Net Area

Subtract total door and window area from total wall area:

Example -- 12x12 bedroom with 8-foot ceilings:

• Total wall area: 2 x (12 + 12) x 8 = 384 sq ft
• One door: 21 sq ft
• Two windows: 2 x 12 = 24 sq ft
• Net area: 384 - 21 - 24 = 339 sq ft

Step 4: Add Waste Factor and Divide by Sheet Size

Apply 10% waste and divide by your sheet area:

• With waste: 339 x 1.10 = 373 sq ft
• Using 4'x8' sheets (32 sq ft each): 373 / 32 = 11.7 = 12 sheets
• Using 4'x12' sheets (48 sq ft each): 373 / 48 = 7.8 = 8 sheets

Common Room Examples

12x12 Bedroom (standard)

Walls: 384 sq ft. Subtract 1 door + 2 windows = 45 sq ft. Net: 339 sq ft. With 10% waste: 12 sheets (4'x8') or 8 sheets (4'x12'). Add ceiling: 144 sq ft = 5 more sheets (4'x8'). Screws: ~483. Joint tape: ~121 ft. Joint compound: ~25.6 gallons.

10x15 Living Room

Walls: 2 x (10 + 15) x 8 = 400 sq ft. Subtract 1 door + 3 windows = 57 sq ft. Net: 343 sq ft. With 10% waste: 12 sheets (4'x8'). Estimated cost at $14/sheet: $168. With materials (screws, tape, compound): approximately $240-$280 total.

20x25 Basement

Walls: 2 x (20 + 25) x 8 = 720 sq ft. Subtract 1 door + 4 small windows = 69 sq ft. Net: 651 sq ft. With 10% waste: 23 sheets (4'x8') or 15 sheets (4'x12'). Add ceiling (500 sq ft): 17 more 4'x8' sheets. Total for walls + ceiling: 40 sheets. At $14/sheet: $560.

10x10 Home Office

Walls: 2 x (10 + 10) x 8 = 320 sq ft. Subtract 1 door + 1 window = 33 sq ft. Net: 287 sq ft. With 10% waste: 10 sheets (4'x8'). This is a small enough project for a confident DIYer to complete in a weekend.

14x18 Master Bedroom

Walls: 2 x (14 + 18) x 8 = 512 sq ft. Subtract 2 doors + 3 windows = 78 sq ft. Net: 434 sq ft. With 10% waste: 15 sheets (4'x8') or 10 sheets (4'x12'). Using 4'x12' sheets saves 5 sheets and significantly reduces taping time.

Don't Forget the Ceiling

If you're also drywalling the ceiling, calculate it separately: Ceiling Area = Room Length x Room Width. Use 5/8" drywall for ceilings -- the extra thickness prevents sagging between joists. Ceiling drywall should always be installed before wall drywall, so that the wall sheets support the ceiling edges.

Materials Beyond Drywall Sheets

A complete drywall project requires more than just sheets. Here's what you'll need:

• Drywall screws: Approximately 1 screw per square foot. Use 1-1/4" screws for 1/2" drywall and 1-5/8" screws for 5/8" drywall.
• Joint tape: About 1 foot of tape per 4 square feet of drywall. Paper tape provides stronger joints; mesh tape is easier for beginners.
• Joint compound (mud): Approximately 0.053 gallons per square foot for three coats. A 4.5-gallon bucket covers about 85 sq ft.
• Corner bead: One piece per outside corner. Metal or paper-faced beads are both acceptable.
• Sandpaper: 120-grit for rough sanding between coats, 150-grit for final smoothing.

Cost Factors

The total cost of a drywall project includes:

• Drywall sheets: $10-$24 per sheet depending on size and thickness.
• Screws: About $8-$12 per box of 1,000 (enough for ~30 sheets).
• Joint compound: $12-$18 per 4.5-gallon bucket.
• Joint tape: $4-$8 per 250-foot roll.
• Professional installation: $1.50-$3.50 per square foot for hanging, taping, and finishing.
• Delivery: Many suppliers offer free delivery for orders of 50+ sheets. Smaller orders may incur a $50-$100 delivery fee.

Try the Calculator

Skip the manual math and use our free drywall calculator below. Select your room type, enter dimensions, choose your sheet size and thickness, and get a complete materials list instantly.