Drywall Calculator
Estimate drywall sheets, screws, and joint compound from total wall and ceiling area.
Estimates are for planning. Confirm quantities against your measured site and product packaging before ordering, and follow local building codes.
How to measure for drywall
Measure each wall’s length, multiply by its height, and add the walls together. For a standard rectangular room that’s two lengths plus two widths, times ceiling height. Doing the ceiling too? Add length times width once more.
A 12×12 bedroom with 8 foot ceilings works out to 4 walls × 12 feet × 8 feet = 384 square feet of wall, plus 144 for the ceiling, 528 total. Closets count too, and people forget them constantly: a reach-in closet adds three more wall surfaces plus its own little ceiling, easily another 100 square feet.
Leave doors and windows in the count unless they’re huge. The cutouts rarely become usable pieces, and the extra acts as your cushion for broken corners and bad cuts. For a garage door or a sliding-glass wall, go ahead and subtract.
Note your stud spacing and ceiling height while you’re at it. Walls taller than 8 feet usually mean 4×10 or 4×12 sheets hung horizontally, or 54 inch wide board made specifically for 9 foot walls. And decide sheet orientation now: horizontal hanging on walls puts the long joint at a comfortable taping height and crosses more studs per sheet.
The formula and what it assumes
The calculator takes your total area, adds 10% for waste, divides by the area of your chosen sheet, and rounds up to a whole sheet: sheets = ceiling of (area × 1.10 ÷ sheet area). Sheet areas are 32 square feet for 4×8, 40 for 4×10, and 48 for 4×12.
The 528 square foot bedroom above: 528 × 1.10 = 581, divided by 32 is 18.2, round up to 19 sheets of 4×8.
Screws are estimated at 32 per sheet, which reflects common 16 inch spacing along each stud on walls. Ceilings fastened at 12 inch spacing will run higher, so treat the screw count as a floor if you’re boarding overhead.
Joint compound is figured at 0.053 pounds per square foot of board, a standard industry estimating rate for taping plus two finish coats. The bedroom needs about 28 pounds, so one 4.5 gallon bucket covers it with plenty left over.
The 10% waste assumption fits ordinary rooms. Angled ceilings, lots of small closets, or curved walls chew up board faster, so bump your area up before entering it if your room is complicated.
Buying tips
US stores stock drywall in 4×8, 4×10, and 4×12 sheets, in 1/4, 3/8, 1/2, and 5/8 inch thicknesses. Half-inch is the standard for walls. Many codes require 5/8 inch Type X (fire-rated) on garage walls and ceilings that adjoin living space, and 5/8 also resists sagging on ceilings with 24 inch joist spacing. Bathrooms get moisture-resistant board (the green or purple-faced product) on walls, with cement board behind tile in wet areas.
A 1/2 inch 4×8 sheet weighs around 50 pounds and a 4×12 around 75, so think about logistics before you fall in love with big sheets. Lightweight 1/2 inch board shaves roughly a quarter of that weight and hangs the same.
For a whole-room job or bigger, delivery earns its fee. Big-box stores deliver curbside; drywall suppliers will often carry board into the house and stack it where you’re working, which is worth a lot when the job is upstairs. Pros order from suppliers for exactly that reason.
Buy your tape, corner bead, and screws in the same trip. Paper tape is stronger for inside corners; mesh tape is easier for flat joints with setting-type compound. For compound, all-purpose in the 4.5 gallon bucket is the safe default, and the bucket itself becomes your mixing and tool-washing station.
One sheet of scrap is normal. Zero scrap means you measured wrong.
Frequently asked questions
Should I subtract doors and windows from my drywall measurement?
Usually not. The board you cut out for a window often can't be reused elsewhere, since you need full-height pieces and unbroken edges for clean joints. Skipping the subtraction builds in a natural cushion. The exception is a big opening like a garage door or a wall of windows, where it's fair to subtract most of it.
What size drywall sheet should I buy?
4×8 sheets (32 square feet) are the default because one person can carry and hang them. If your walls are longer and you have help, 4×12 sheets (48 square feet) mean fewer joints to tape, and fewer joints is the single biggest finishing time-saver. Use 1/2 inch thickness for walls; ceilings and garage walls adjoining living space often call for 5/8 inch Type X, so check your local code.
How many screws does drywall need?
Plan on about 32 screws per 4×8 sheet, which matches typical spacing of one screw every 16 inches on walls along each stud. Ceilings use tighter 12 inch spacing, so figure more there. Use coarse-thread drywall screws for wood framing, 1-1/4 inch for 1/2 inch board.
How much joint compound do I need?
Figure about 0.053 pounds per square foot of board for a standard three-coat tape job, so a 500 square foot room needs roughly 27 pounds. Buckets sell in 1 gallon, 3.5 gallon, and 4.5 gallon sizes. Buy all-purpose for taping; a lightweight topping or all-purpose works for finish coats.