Drywall Calculator: How Many Sheets Do I Need?
Drywall comes in big sheets, and estimating them by eye is how beginners end up with a half-finished ceiling on a Sunday night. This free drywall calculator measures your walls and ceiling, subtracts the doors and windows you will not be boarding over, adds the standard waste allowance for offcuts, and tells you exactly how many sheets of 4 × 8, 4 × 12 or 4 × 16 drywall to buy — plus an estimate of screws and total cost.
Drywall Sheet Calculator
How to Use This Drywall Calculator
Measure the room's length, width and wall height in feet. The calculator finds the wall area with perimeter × height, adds the ceiling (length × width) if you are boarding it, and subtracts your openings.
Estimate your door and window area in square feet — a standard interior door is about 21 square feet, a typical window 15 square feet, and a 12 × 12 room with one door and two windows comes to 51. Pick your sheet size: 4 × 8 is easiest to handle alone, 4 × 12 means fewer seams to tape. Check the box to include the ceiling or leave it unchecked for walls only, then click Calculate.
The Drywall Calculation Formula
The wall area is 2 × (length + width) × height, the ceiling is length × width, and total area = walls + ceiling − openings. Add 10% for offcuts with area × 1.10, then divide by the sheet area: sheets = total ÷ sheet area, rounded up.
Worked example: a 12 × 12 room with 8-foot walls has 384 square feet of wall plus a 144-square-foot ceiling — 528 square feet. Subtract 51 square feet of openings for 477, add 10% waste: 477 × 1.10 = 524.7. At 32 square feet per 4 × 8 sheet, 524.7 ÷ 32 = 16.4 — so you buy 17 sheets. Screw estimate: about one screw per square foot, so roughly 525 screws (about 6 pounds).
Pro Tips for Hanging Drywall
Hang the ceiling first, then the walls — the wall sheets help hold the ceiling edges tight. Stagger the joints between rows so four corners never meet at one point; a running-brick pattern is far stronger and easier to tape.
Use 5/8-inch board on ceilings to prevent sagging between joists (many codes require it), and moisture-resistant board in bathrooms. Budget for the finishing materials too: joint compound, tape, corner bead and primer usually cost about as much as the board itself.
Frequently Asked Questions
How many sheets of drywall do I need for a 12x12 room?
A 12x12 room with 8-foot walls has 384 sq ft of wall plus 144 sq ft of ceiling — 528 sq ft total. With a 10% waste allowance that is 580.8 sq ft, which takes 19 sheets of 4x8 drywall (32 sq ft each).
How many drywall screws do I need per sheet?
Plan for about one screw per square foot of drywall — roughly 32 screws per 4x8 sheet on walls with 12-inch spacing, a few more on ceilings where spacing should be 12 inches on center.
Should I use 4x8 or 4x12 drywall?
4x12 sheets create fewer seams to tape and finish, which means a faster, smoother job — but they are heavy and awkward to handle alone. 4x8 sheets are manageable solo and fit smaller rooms with less waste.
What thickness drywall should I use?
Use 1/2-inch drywall for most walls. Ceilings should be 5/8-inch, which resists sagging between joists and is required by many building codes for fire separation.