Drywall Calculator

Drywall Calculator: How Many Sheets Do I Need?

Drywall is bought by the sheet, but rooms are measured in square feet, and the sheet that is easy to carry is not always the sheet that covers a wall fastest. If you are asking how many sheets of drywall do i need, the honest answer starts with the whole surface — the walls and, usually, the ceiling — takes away the large openings, and then adds something back for cuts and mistakes. This page does that arithmetic in imperial or metric units and shows every formula it uses, so you can check the result with a pencil before you order.

Quick answer

For a 12 × 12 ft room with an 8 ft ceiling, you need 17 sheets of 4 × 8 ft drywall for the walls and ceiling, before waste. The table below gives the same figure for other common room sizes. Every total covers all four walls plus the ceiling at 8 ft, deducts nothing for doors or windows, and adds nothing for waste — use the calculator underneath the table for those adjustments.

Room size	Walls + ceiling area	Sheets of 4 × 8 ft
10 × 10 ft	420 sq ft	14
12 × 12 ft	528 sq ft	17
12 × 16 ft	640 sq ft	20
16 × 20 ft	896 sq ft	28
20 × 20 ft	1,040 sq ft	33

Check a row by hand: a 12 × 12 ft room has 528 sq ft of wall and ceiling, and one 4 × 8 ft sheet covers 32 sq ft, so 528 ÷ 32 = 16.5, which rounds up to 17 sheets — you cannot buy half a sheet.

How the calculation works

The calculator follows the same steps a contractor works through on a notepad, in the same order. First it finds the total surface area. In Room mode, the walls are the room's perimeter — twice the length plus twice the width — multiplied by the ceiling height, and the ceiling is simply length × width, added if you leave the ceiling box ticked. In Area mode it skips that step and starts from a total area you enter yourself, which is useful for a single wall, an L-shaped room, or a surface you have already measured. Counting the walls and ceiling together matters because most rooms are boarded as one job — the ceiling is not optional extra area, and it is usually the first surface hung.

• Total area (Room mode): (2 × length + 2 × width) × ceiling height, plus length × width if the ceiling is included.
• Net area: total area − (doors × 21 sq ft) − (windows × 15 sq ft). In metric, each door deducts 1.95 m² and each window 1.4 m².
• Sheets needed (net): net area ÷ sheet coverage, rounded up to a whole sheet.
• Sheets to buy: net area × (1 + waste %) ÷ sheet coverage, rounded up.
• Screws: sheets to buy × 36, also shown as a weight at roughly 280 screws per lb (about 617 per kg in metric).
• Joint compound: one 4.5-gallon bucket per 400 sq ft of net area, rounded up — in metric, roughly one 19 kg tub at the same rate.
• Joint tape: net area × 0.4 gives the length of tape; divided by 250 ft per roll, rounded up (90 m rolls in metric).

Why do most pros not deduct small windows? Because a window opening is rarely free area. The board around it gets cut into narrow strips, the corners need extra pieces, and the offcut from the opening seldom fits anywhere useful — so the waste created around it roughly cancels out the area it saves, and many estimators leave small windows in the total. Large openings are different: a wide doorway, an open-plan gap or a big picture window really does remove whole sheets, which is why this calculator lets you enter doors and windows and decide for yourself.

The waste allowance is separate from openings, and it earns its place. It covers the cuts at edges and corners, sheets chipped or broken in transit or while being carried in, and the inevitable sheet that gets measured once and cut wrong. Ten percent suits a simple rectangular room with full sheets landing neatly; rooms with angles, alcoves or a lot of short walls deserve more.

Worked example

Take a 12 × 12 ft room with an 8 ft ceiling, boarded on the walls and the ceiling, with no openings deducted and 4 × 8 ft sheets. Here is every step, using the same formulas as the calculator above.

• Step 1 — walls: the perimeter is 12 + 12 + 12 + 12 = 48 ft, and 48 × 8 ft = 384 sq ft of wall.
• Step 2 — ceiling: 12 × 12 = 144 sq ft.
• Step 3 — total area: 384 + 144 = 528 sq ft.
• Step 4 — sheets (net): ceil(528 ÷ 32) = ceil(16.5) = 17 sheets.
• Step 5 — with 10% waste: ceil(528 × 1.10 ÷ 32) = ceil(18.15) = 19 sheets to buy.

Now deduct one standard door and one window from the same room. A door takes away 21 sq ft and a window 15 sq ft, so the net area is 528 − 21 − 15 = 492 sq ft. Sheets (net) become ceil(492 ÷ 32) = ceil(15.375) = 16 sheets. Set the calculator to those same figures — one door, one window, waste at 0% if you want the net count — and it returns exactly those numbers, which is the quickest way to confirm your own settings are doing what you expect.

Sheet sizes and types

The 4 × 8 ft sheet is the DIY standard for a practical reason: one person can usually carry it, turn it in a hallway, and get it up a flight of stairs without help. The 4 × 10 and 4 × 12 ft sheets cover a wall faster and leave fewer joints to tape and finish, which is why professionals reach for them on long, straight runs — but they are heavy, awkward on stairs and in tight corners, and genuinely difficult to handle alone or overhead. Fewer joints is only a saving if the sheet arrives on the wall in one piece.

• Thickness: ½ in board is the standard for most walls, and it is what the common sheet sizes above assume.
• Fire rating: ⅝ in Type X board is fire-rated and is commonly required in garages and where a fire separation is needed between a garage or another unit and the living space.
• Moisture: moisture-resistant board suits bathrooms and other humid rooms, but it does not belong inside a shower enclosure — a tiled shower needs cement board behind the tile, not drywall of any kind.
• Ceilings: where joists are spaced 24 in apart, use a ceiling-rated board or ⅝ in board — standard ½ in wall board can sag between wide-spaced supports over time.
• UK and Australia: the same product is sold as plasterboard. The standard sheet there is 1200 × 2400 mm, usually 12.5 mm thick, which is why the metric side of the calculator works in those sizes.

Hanging tips in brief

• Order of work: hang the ceiling first, then the walls from the top down, so the wall sheets support the edges of the ceiling sheets.
• Stagger joints: offset the butt joints from row to row. Seams that line up in a continuous cross are weaker and much harder to finish invisibly.
• Mind the floor gap: keep every sheet ¼ to ½ in off the floor. The gap stops the board wicking up moisture and is covered later by the skirting board or baseboard.
• Screw pattern: screws about every 12 in across the field of a sheet and every 8 in along the edges and on ceilings, driven just below the paper surface without tearing it.
• Work overhead safely: renting a panel lift makes ceiling work far easier and safer. It holds the sheet flat and tight to the joists while you fix it, instead of you balancing it on your head.

Frequently asked questions