SiteScope Tech
Skip the tape measure: scan the room with an iPhone Pro and get exact wall areas. See how it works.
Free Tool

Drywall Calculator

Enter your walls and ceiling, subtract doors and windows, and pick a sheet size. Get the number of drywall sheets plus approximate screws, tape and joint compound.

1 Walls

Room length
ft
in
Room width
ft
in
Ceiling height
ft
in

2 Ceiling

Ceiling area uses the room length × width above.

3 Openings (subtracted from the walls)

Doors
qty
in W
in H
Windows
qty
in W
in H

Sizes in inches. A standard interior door opening is about 36 × 80 in. Set a quantity to 0 to skip it.

4 Sheet Size & Waste

Sheet size
%
Quick set:

About 10% for simple rooms, 15% or more with many openings, angles or soffits.

Results

Gross wall area
Openings
Net wall area
Ceiling area
Waste
Wall sheets
Ceiling sheets
Sheets to buy
sheets
Finishing supplies (rules of thumb)
Drywall screws
Joint tape
Joint compound

Approximate. Based on common rules of thumb: about 1 screw per sq ft of board on walls and 1.25 on ceilings, about 370 ft of paper tape and about 10 gal of ready-mixed compound per 1,000 sq ft for a standard three-coat finish. Framing spacing, finish level and your crew change these numbers.

Estimates only. Sheet counts are by area and don't lay out each wall. Check local code and the board manufacturer's instructions before ordering.

How to calculate how much drywall you need

Find the wall area (room perimeter × ceiling height), subtract doors and windows, add the ceiling (length × width), add about 10% waste, then divide by the area of one sheet and round up. A 4 × 8 sheet covers 32 sq ft, a 4 × 10 covers 40 sq ft and a 4 × 12 covers 48 sq ft.

Wall area = 2 × (Length + Width) × Height
Net wall area = Wall area − doors − windows
Ceiling area = Length × Width
Sheets = (Area × (1 + waste %)) ÷ sheet area (round up)

Worked example

A 12 × 14 ft bedroom with 8 ft ceilings, one 36 × 80 in door and two 36 × 48 in windows, hung with 4 × 8 sheets and 10% waste.

  1. Wall area: 2 × (12 + 14) × 8 = 416 sq ft.
  2. Openings: door 36 × 80 ÷ 144 = 20 sq ft, windows 2 × (36 × 48 ÷ 144) = 24 sq ft, total 44 sq ft.
  3. Net wall area: 416 − 44 = 372 sq ft.
  4. Wall sheets: 372 × 1.10 ÷ 32 = 12.79, round up to 13 sheets.
  5. Ceiling: 12 × 14 = 168 sq ft. 168 × 1.10 ÷ 32 = 5.78, round up to 6 sheets.
  6. Total: 19 sheets of 4 × 8 drywall. By the rules of thumb, that's about 590 screws, 200 ft of tape and 5.4 gal of compound (two 4.5 gal pails).

Round wall and ceiling sheets up separately. Ceilings often use a different board (sag-resistant or 5/8 in), so it helps to order them as their own line. Painting after you hang? The paint calculator uses the same net wall area.

Skip the tape measure

Scan the room. Get every wall, door and window measured.

SiteScope uses the LiDAR sensor on iPhone Pro and iPad Pro to scan a room and build a measured floor plan with walls, doors and windows placed. Takeoffs show gross and net wall area, with the openings already subtracted, so you are not adding up walls on a notepad.

  • Wall lengths, ceiling heights and openings from one scan
  • Gross vs net areas per wall in the takeoff
  • Photo documentation and PDF reports from the same project
Start for free How 3D room scanning works

Scanning needs an iPhone Pro or iPad Pro with LiDAR.

Wall areas from a scan (example)
Wall 1 · 12' 0" × 8' 0"96 sq ft
Wall 2 · 14' 0" × 8' 0", 1 door92 sq ft
Wall 3 · 12' 0" × 8' 0", 2 windows72 sq ft
Wall 4 · 14' 0" × 8' 0"112 sq ft
Net wall area372 sq ft

Drywall Calculator FAQ

How many sheets of drywall do I need for a 12x12 room?
A 12 x 12 ft room with 8 ft ceilings has 384 sq ft of wall (2 x (12 + 12) x 8) and 144 sq ft of ceiling. With 10% waste and 4 x 8 sheets (32 sq ft each), that is 14 sheets for the walls and 5 for the ceiling, 19 in total, before you subtract any doors or windows.
Should I subtract doors and windows from a drywall estimate?
Subtract doors and large openings, since no board goes there. Many hangers do not subtract small windows, because the piece cut out of the sheet is scrap anyway. For a conservative count, set the window quantity to 0.
Is 4x8 or 4x12 drywall better?
Longer sheets mean fewer butt joints to tape, so 4 x 12 sheets hung horizontally save finishing time on long walls. They are heavy and awkward, so 4 x 8 sheets are easier for one person, small rooms and stairwells. Run the calculator with each size to compare sheet counts.
How many screws do I need per sheet of drywall?
A common rule of thumb is about one screw per square foot of board on walls, so roughly 32 screws for a 4 x 8 sheet, and more on ceilings where the spacing is tighter. Follow the fastening schedule in your local code and the board manufacturer's instructions.
How much joint compound and tape do I need?
As a rule of thumb, plan on about 370 ft of paper tape and about 10 gallons of ready-mixed joint compound per 1,000 sq ft of board for a standard three-coat finish. That works out to one 4.5 gallon pail for roughly every 450 sq ft. Smoother finish levels and skim coats use more.
What waste factor should I use for drywall?
Use about 10% for simple rectangular rooms and 15% or more for rooms with many openings, angled walls, soffits or vaulted ceilings. Cutoffs from one wall rarely fit another, so round up rather than down.

More Free Calculators

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Related Guides

Estimating

How to Turn a Floor Plan into a Material Estimate

From a room scan or blueprint to quantities and a quote.
Takeoffs

From Net Area to Buy Quantity

Why a net area is not an order, and how waste and packaging change it.