Drywall Calculator
Calculate how many sheets of drywall you need for a room, plus screws, joint compound and tape. Supports 4x8, 4x10 and 4x12 sheets with or without the ceiling.
By CalcBuilt Editorial TeamUpdated September 10, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Drywall sheets to buy
- 17 sheets
- 4x8 ft sheets, 478 sq ft plus 10% waste
- Drywall screws
- 526 screws
- About 1.8 lb of 1-1/4 in (32 mm) screws for 1/2 in board, 1-5/8 in (41 mm) for 5/8. Spacing 16 in on walls, 12 in on ceilings (IRC Table R702.3.5)
- Joint compound
- 6 gal
- 2 x 4.5 gal (17 L) buckets. Bed tape and fill with setting-type, finish with lightweight all-purpose
- Joint tape
- 177 ft
- 1 x 500 ft (150 m) rolls. Corner bead is extra: one stick per outside corner
- Total surface area
- 478 sq ft
- 334 sq ft walls + 144 sq ft ceiling. Hang the ceiling first, perpendicular to the joists
Drywall formula
Wall area = 2 x (Length + Width) x Height - openings
Total area = Wall area + Ceiling area (Length x Width)
Sheets = Total area x (1 + waste %) / sheet area (4x8 = 32, 4x10 = 40, 4x12 = 48 sq ft)Worked example
A 16 x 20 ft garage with 9 ft walls, one entry door, one 16 x 7 ft overhead door (112 sq ft) and a ceiling: walls 2 x 36 x 9 = 648 sq ft, minus 132 sq ft of doors = 516 sq ft. Ceiling 320 sq ft. Total 836 sq ft, plus 10% = 920 sq ft. That is 29 sheets of 4 x 8 or 20 sheets of 4 x 12.
Quick reference
| Room size | Total area | 4 x 8 sheets | 4 x 12 sheets |
|---|---|---|---|
| 10 x 10 ft | 370 sq ft | 13 | 9 |
| 12 x 12 ft | 478 sq ft | 17 | 11 |
| 12 x 15 ft | 562 sq ft | 20 | 13 |
| 15 x 20 ft | 810 sq ft | 28 | 19 |
| 20 x 20 ft | 990 sq ft | 35 | 23 |
How to calculate drywall
Find the wall area (perimeter times height) and add the ceiling if you are covering it. Divide by the sheet (32 sq ft for 4x8, 48 for 4x12) and add 10 percent. Waste comes from the layout: every course on a wall that is not a multiple of 4 ft leaves a strip. Most estimators do not deduct standard doors and windows; the cutout is the waste. Deducting them and adding 10 percent, as the defaults do, runs tight, so set both to 0 for a safer count.
A 12 by 12 room with 8 ft walls, one door, two windows and a ceiling has about 478 square feet of surface. With waste that is 17 sheets of 4x8 or 11 sheets of 4x12.
Which sheet size to use
Hang board horizontally, long dimension across the studs, so the seam lands at 4 ft. A 12 ft wall with 4x12 per course has zero butt joints; 4x8 on the same wall leaves a butt joint every 8 ft to feather out. 9 ft walls need 54 in board, two courses make 108 in, or you add a 12 in strip and a third seam. Ceilings go first, perpendicular to the joists, in 5/8 or sag-resistant 1/2.
Use 1/2 inch on walls and 5/8 inch on ceilings at 24 inch joist spacing. A garage ceiling under living space needs 5/8 Type X (IRC R302.6). Screws go 16 inches on walls and 12 on ceilings, 12 on both at 24 inch framing (IRC Table R702.3.5): 1-1/4 inch for 1/2 board, 1-5/8 for 5/8. Greenboard is fine outside the shower. Behind tile in a tub or shower use cement board or foam board; paper-faced gypsum is prohibited there (IRC R702.3.7).
What this calculator leaves out
Corner bead, one 8 ft stick per outside corner and window return. Setting-type compound (Easy Sand 45 or 90) for bedding tape and filling; the all-purpose above is for the finish coats. Cement board for tub and shower walls, primer, and boom delivery to the room, typically $75 to $150, since 4x12 does not ride in a pickup. Type X and 54 in board are not stocked at every yard, so call ahead.
Mistakes that cost money
- 4x8 on 9 ft walls leaves a 12 in strip and a third seam on every wall; order 54 in wide board instead.
- Greenboard behind tub or shower tile fails inspection and rots; IRC R702.3.7 requires cement board or foam board in wet areas.
- Overdriven screws that break the paper hold nothing; use a depth-setting bit and put a second screw beside every one that tore through.
- Regular 1/2 in on a garage ceiling under living space fails inspection; IRC R302.6 calls for 5/8 in Type X there.
- Hauling 4x12 in a pickup snaps sheets over the tailgate; have the yard boom them into the room, typically $75 to $150.
- All-purpose mud for bedding tape shrinks and bubbles; bed and fill with setting-type (Easy Sand 45 or 90), finish with lightweight all-purpose.
Key facts
- A 4 x 8 ft drywall sheet covers 32 sq ft; a 4 x 12 ft sheet covers 48 sq ft.
- Plan on about 1 screw per square foot, or 32 screws per 4 x 8 sheet.
- One 4.5 gallon bucket of joint compound finishes roughly 350 to 400 sq ft of drywall.
- Use 1/2 in drywall on walls and 5/8 in on ceilings and wherever a fire rating is required; a garage ceiling under living space takes 5/8 in Type X (IRC R302.6).
Frequently asked questions
Can I use 4x8 sheets on 9 ft walls?
Two courses of 4x8 make 8 ft, so a 9 ft wall needs a 12 in strip and a third seam on every wall. Order 54 in wide board, where two courses make exactly 108 in. It is a special order at some yards, so call ahead.
How many screws per sheet of drywall?
About 32 screws for a 4x8 sheet on 16 inch stud spacing, roughly one screw per square foot. IRC Table R702.3.5 spaces screws 16 inches on walls and 12 inches on ceilings, 12 inches on both at 24 inch framing. Use 1-1/4 inch screws for 1/2 board and 1-5/8 for 5/8.
How much joint compound per sheet of drywall, and which kind?
Roughly 0.4 gallons per 4x8 sheet for three coats; one 4.5 gallon bucket finishes about 10 to 12 sheets. Bed the tape and fill with setting-type (Easy Sand 45 or 90) and use lightweight all-purpose for the finish coats.
Sources and references
Next steps for this project
The usual order for a paint & walls project. See all paint & walls calculators.
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Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.