Drywall calculator
This divides the area you enter by a sheet's area and rounds up. It does not read a plan or deduct openings for you — subtract large openings yourself, and confirm the count against the actual room before you order.
Enter the size of a wall or ceiling and how many surfaces of that size you have, pick a sheet, and the tool totals the area, divides by the sheet area, adds waste and rounds up to whole sheets. That rounded number is what you buy.
Ejemplo resuelto
A room with four 12 ft × 8 ft walls is 4 × 96 = 384 square feet. Using 4×8 sheets at 32 ft² each, that is 384 ÷ 32 = 12 sheets before waste. Add 10% and round up and you are buying 14 sheets. Switch to 4×12 sheets and the same wall area needs 384 ÷ 48 = 8 before waste, 9 after.
In metric: four 3.6 m × 2.4 m walls are 4 × 8.64 = 34.56 m². A 1200 × 2400 mm sheet covers 2.88 m², so that is 12 sheets before waste; with 10% it is 34.56 × 1.1 ÷ 2.88 = 13.2, so 14 sheets.
En la obra
A bedroom, walls and lid. 12 ft × 14 ft with 8 ft ceilings. The walls are the perimeter times the height: 2 × (12 + 14) × 8 = 416 ft². The ceiling is 12 × 14 = 168 ft². That is 584 ft² all in; with 10% and 4 × 8 sheets it is 584 × 1.1 ÷ 32 = 20.1, so 21 sheets. In 4 × 12s it is 13.4 — 14 sheets — and on a 12 ft wall two 12-footers stacked flat run corner to corner with no butt joint to tape. Fewer sheets, fewer joints, heavier lift: pick with the help you have. In metric, a 3.6 × 4.2 m room with a 2.4 m ceiling is 2 × (3.6 + 4.2) × 2.4 = 37.44 m² of wall plus 15.12 m² of ceiling — 52.56 m², × 1.1 ÷ 2.88 = 20.1, so 21 sheets of 1200 × 2400.
A garage with the big door taken off. 24 × 24, 9 ft walls, no ceiling. Perimeter 96 ft × 9 = 864 ft², less a 16 × 7 overhead door = 112 ft², so 752 ft² to board. At 4 × 12 with 10%: 752 × 1.1 ÷ 48 = 17.2 → 18 sheets. Leave the door in the area and you carry two sheets more than you will hang. The man door and the window stay in; they are the waste.
Counting by rows instead of area. A 40 ft wall, 8 ft high, boarded horizontally is two rows of 40 ft. In 12 ft sheets each row is 3⅓ sheets — three full and a 4 ft piece, and the 8 ft offcut from the fourth sheet starts the second row. Seven sheets. The area method says 320 ÷ 48 = 6.7 → 7. When the two methods agree you can order; when they do not, the row method is telling you about a layout problem the area cannot see.
What went wrong?
Quick referencefor boarding
- Sheet areas
- 4 × 8 = 32 ft² · 4 × 9 = 36 · 4 × 10 = 40 · 4 × 12 = 48 · 54 in × 12 ft = 54
- Wall area of a room
- perimeter × ceiling height
- Ceiling
- length × width — one more surface, often a different sheet
- Sheets per 100 ft², before waste
- 4 × 8: 3.1 · 4 × 12: 2.1
- Sheets per 10 m², before waste
- 1200 × 2400: 3.5 · 1200 × 3600: 2.3
- A standard door opening
- about 21 ft² (2 m²) · a 16 × 7 overhead door is 112 ft² (10.4 m²)
- Metric sheet
- 1,200 × 2,400 mm = 2.88 m² · 1,200 × 2,700 = 3.24 m² · 1,200 × 3,000 = 3.6 m² · 1,200 × 3,600 = 4.32 m²
Waste & overagewhat to add, and why
- Board hangers add 10% on a room of plain walls and 15–20% for sloped ceilings, bulkheads and closets, because every cut around a window or a pot light wastes the offcut. It goes in the waste field.
- Sheets sell by the pair (bundled two together); the buy line gives sheets, so round to an even number for a bundled delivery.
- If the room needs both 8 ft and 12 ft sheets, run it twice — once per sheet size — instead of averaging.
Mistakes to catchbefore you order
- Typing the floor area instead of the wall area — the surfaces field wants each wall (and ceiling) as length × height.
- Deducting the doors and windows: hangers rarely do, because the board around an opening is cut from a full sheet anyway; let the waste figure cover them.
- Measuring the ceiling length along a sloped ceiling as if it were flat — use the sloped length, which is longer.
What an inspector looks forthe building inspector, where the board is doing a fire or structural job
On this part of the job
- Board type and thickness where a rated assembly is involved. A fire separation, a garage-to-house wall, a shaft or a ceiling under habitable space are each a specific assembly, and the assembly listing names the board.
- That a rated assembly is built exactly as its listing shows — layers, orientation, joint stagger, framing spacing and fastener pattern are all part of the listing, and changing any of them voids it.
- Fastener spacing at edges and in the field, and screws set without breaking the face paper.
- Firestopping and sealing at the top and bottom of rated walls, and around every penetration through them.
- Board carried through to the deck above on a wall that has to be continuous, rather than stopping at the suspended ceiling.
Have this ready
- The drawing's wall-type schedule and the assembly listing for each rated wall.
- A box or two left with their labels, so the board type can be read.
- The rated walls left unpainted or marked so they can be identified.
Every figure an inspector measures against comes from the code your jurisdiction has adopted, the stamped drawing, or the manufacturer's printed instructions — so none of them are printed here. Look the number up in your own book, type it into the tool, and the arithmetic is yours.
La fórmula
sheets = (total area × (1 + waste)) ÷ sheet area, rounded up
Total area is the surface length times height times the number of surfaces. Dividing by one sheet's area gives a fractional sheet count; the waste factor covers the offcuts, and rounding up turns it into whole sheets you can actually buy.
Preguntas
- How many sheets of drywall do I need?
- Work out the total surface area of the walls and ceilings, then divide by the area of one sheet and round up. A 4×8 sheet covers 32 square feet; a 4×12 covers 48. In metric a 1200 × 2400 mm sheet covers 2.88 m². This tool does the division for you once you enter the area and pick a sheet size, and it adds a waste factor for cuts.
- What size drywall sheet should I use?
- Bigger sheets mean fewer seams to tape, which is faster and looks better, but they are heavier and harder to handle in tight spaces. 4×8 is the easy-to-carry standard; 4×12 is common on long walls and ceilings with a lift or a second pair of hands. Metric yards sell 1200 × 2400 as the standard, with 2700, 3000 and 3600 lengths for tall walls and ceilings. Pick the size in the tool and the count adjusts.
- Do I subtract windows and doors?
- You can, but many hangers do not bother for small openings — the offcuts rarely make a full sheet and the waste factor absorbs them. For big openings like a garage door or a wall of glass, subtract them from the area you enter so you are not buying sheets you will never hang.
- How much waste should I allow for drywall?
- Around 10% is typical, which is the default here. Bump it up for a room full of angles, closets and short walls, where you cut more and waste more, and you can trim it down on a big open rectangle where full sheets go up with little offcut.
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