Drywall Calculator
This drywall calculator turns your room’s length, width and ceiling height into the number of 4×8, 4×10 or 4×12 sheets to buy, with the 10% waste allowance shown on its own line. It also estimates joint tape, ready-mix compound and screws using standard industry rules of thumb, and works in feet or meters.
Drywall sheets needed
15sheets
- Area to cover412 sq ft
- Before 10% waste13 sheets (+2 waste)
- Joint tape (≈37 ft per 100 sq ft)153 ft
- Joint compound (≈0.137 lb/sq ft)57 lb ≈ 1 × 4.5-gal bucket
- Screws (≈1 lb per 300 sq ft)2 lb
Formulas last reviewed on .
How the sheet count is calculated
The calculator first works out the area to cover, then divides it by your sheet size and adds waste:
sheets = ceil(area ÷ sheet area × 1.10)
Two times length-plus-width is the room’s perimeter, and multiplying by height gives the wall area. Each door earns a 21 sq ft credit (a standard 3×7 slab) and each window 15 sq ft — you don’t hang board over openings, though you’ll still trim around them. If you toggle the ceiling on, length × width is added.
Dividing by the sheet area — 32, 40 or 48 sq ft — and multiplying by 1.10 builds in 10% for offcuts and breakage before rounding up to a whole sheet. The finishing estimates are industry rules of thumb, not exact takeoffs: roughly 37 feet of joint tape per 100 sq ft of board, one 4.5-gallon bucket of ready-mix compound per ~450 sq ft (a bucket weighs about 61.5 lb, so ≈0.137 lb per square foot), and a pound of screws per 300 sq ft.
Worked example: rocking a 16 × 12 garage office
Say you’re converting the back of a garage into a 16 × 12 ft office with standard 8-foot walls. The ceiling already has finished board, so it’s walls only — one entry door, one window, hung with 4×8 sheets. Those are the calculator’s defaults, so the result box above shows this exact job.
- Wall area: 2 × (16 + 12) × 8 = 448 sq ft.
- Opening credits: one door (−21) and one window (−15) take it to 412 sq ft.
- Sheets: 412 ÷ 32 = 12.9, so 13 sheets would technically cover it.
- Waste: 12.9 × 1.10 = 14.2, rounded up to 15 sheets to buy — the two extra sheets absorb the L-cuts around the door and window and the inevitable snapped corner.
- Finishing: 412 × 0.37 ≈ 153 ft of tape; compound at 61.5 lb per 450 sq ft is 412 × 0.137 ≈ 57 lb (one 4.5-gal bucket); and 412 ÷ 300 ≈ 2 lb of screws.
So the shopping list is 15 sheets, one bucket of mud, a 250-ft roll of tape and a 2-lb box of coarse-thread screws. Buy the full 15 — a delivery with 13 sheets and no spare is how projects stall on a Sunday afternoon.
How many sheets of drywall do I need for a 10×10 to 20×20 room?
The table covers common room sizes with 8-foot ceilings, walls only, before door and window credits. The 10% waste allowance is already included, so these are buy-this-many numbers — subtract roughly one sheet per door and half a sheet per window if your room has several.
| Room size | 4×8 sheets | 4×12 sheets |
|---|---|---|
| 10 × 10 ft | 11 | 8 |
| 12 × 12 ft | 14 | 9 |
| 12 × 16 ft | 16 | 11 |
| 14 × 16 ft | 17 | 11 |
| 16 × 16 ft | 18 | 12 |
| 16 × 20 ft | 20 | 14 |
| 20 × 20 ft | 22 | 15 |
Notice how the 4×12 column runs roughly a third lower. Longer sheets don’t just mean fewer trips up the ladder — every sheet you eliminate removes a butt joint, and butt joints are the hardest seams to mud flat. If your walls run 12 feet or more and you can physically get 12-footers into the room, they’re worth the awkward carry.
Frequently asked questions
Should I buy 4×8 or 4×12 drywall sheets?
Buy the longest sheet you can maneuver into the room and lift safely. A 4×12 spans a whole 12-foot wall in one piece, which eliminates butt joints — the seams where two cut ends meet, which sit proud and are slow to feather out. That said, a 4×12 weighs around 80 lb and won’t turn the corner in most hallways or stairwells. For one person working alone in a finished house, 4×8s are usually the realistic choice.
Should drywall be hung vertically or horizontally?
On residential walls, hang it horizontally. Running sheets across the studs puts the long seam at a comfortable 4-foot working height, cuts total seam length in most rooms, and bridges more studs, which stiffens the wall and hides studs that aren’t perfectly straight. Vertical hanging makes sense for walls under 4 feet wide and in commercial work where fire codes require seams to land on framing their full length.
What thickness of drywall should I use on a ceiling?
Use 5/8-inch on ceilings whenever joists are 24 inches on center — half-inch board will sag into a visible wave between them, especially under attic insulation. On 16-inch centers you can use half-inch, but many pros still prefer 5/8 or a “sag-resistant” half-inch ceiling board. This calculator counts sheets by area either way; just price the thicker board when you toggle the ceiling on.
How much joint compound and tape do I need per sheet?
Plan on about 0.137 lb of ready-mix compound per square foot of board — call it 4.4 lb per 4×8 sheet, or one 61.5-lb, 4.5-gallon bucket per 450 sq ft — and roughly 37 feet of tape per 100 sq ft. These are the industry rules of thumb this calculator uses, and they assume a standard three-coat finish. Textured finishes and bad framing both eat more mud, so round up to the next bucket if you’re unsure.
Does the calculator subtract doors and windows?
Yes — each door removes 21 sq ft (a standard 3 × 7 ft opening) and each window 15 sq ft. That’s deliberately a partial credit: you still waste board making the L-shaped cuts around openings, and small windows barely save a usable piece. If your room has a sliding patio door or a picture window, count it as two doors or two windows to keep the estimate honest.
These results are planning estimates only — verify quantities with your supplier and local building code before you buy or build. See our terms of use.