To work out how much drywall you need, add up the area of every wall and ceiling you are covering, add about 10 percent for waste, divide by the area of one sheet (32 square feet for a 4 by 8, 48 for a 4 by 12) and round up. A 12 by 12 foot basement room with 8 foot walls is about 528 square feet, so plan on 19 sheets of 4 by 8 or 12 sheets of 4 by 12.
How much drywall do I need? The four-step formula
The same four steps work for any room.
- Walls: multiply the distance around the room by the ceiling height.
- Ceiling: multiply the room's length by its width.
- Add them together, then multiply by 1.10 to cover waste.
- Divide by the area of one sheet and round up to a whole sheet.
As one line: sheets = (wall area + ceiling area) x 1.10 / area of one sheet. That is all a drywall calculator does behind the screen. Stud and joist spacing do not change the sheet count. They change how many screws you need.
Work in one unit. A 4 by 8 foot sheet is 1.2 by 2.4 m, close to 3 square metres. One square metre is about 10.76 square feet, so convert before you mix numbers from a flyer with numbers from a tape measure.
How to measure walls and ceilings
- Sketch each room and write every length on it. Measure to the framing, not to the old finished surface.
- Walls: measure each wall's length and height, or take the perimeter once if the height is the same all around. Basement ceiling heights vary from house to house, so measure instead of assuming 8 feet.
- Ceilings: length times width. Count bulkheads that hide ducts and pipes as extra surface, because each one has a bottom and two sides.
- Openings: most estimators ignore a regular door or small window, since the cut-out piece is rarely reusable. Subtract only large openings such as a patio door or wide archway.
- Stairwells, closets and soffits get measured on their own. Add them to the total.
- Taller walls: for 9 foot ceilings, ask your supplier about 54 inch (1.37 m) wide board. It runs sideways on the wall and covers the full height with one horizontal joint.
Round every measurement up to the next 25 mm (1 in). It is easier to return a sheet than to drive back for one.
4 by 8 or 4 by 12 sheets: which to choose
Longer sheets mean fewer seams to tape. They are also heavier and harder to carry.
| Sheet size | Area | Choose it if | Watch for |
|---|---|---|---|
| 4 by 8 ft (1.2 by 2.4 m) | 32 sq ft | Hanging alone or in tight spaces, small rooms, anything coming down a basement stair | More butt joints on long walls and ceilings |
| 4 by 10 ft | 40 sq ft | Longer walls where 8 ft leaves an extra joint | Less common stock, awkward to carry |
| 4 by 12 ft (1.2 by 3.7 m) | 48 sq ft | Long walls and ceilings where one sheet spans the room | Heavy: a 1/2 inch sheet weighs roughly 35 kg (80 lb). Needs two people and a clear path |
Measure the stair, the turn at the bottom and the doorway before you order 12 footers for a basement. Sheets that will not make the corner end up cut in half in the driveway.
The right length also depends on the framing. Joints should land on studs or joists, so a good layout often comes from a sketch of where the seams fall, not from the sheet count alone. Our guide to hanging drywall covers layout and stagger.
Worked example: how much drywall for a 12 by 12 room
Take a 12 by 12 foot (3.7 by 3.7 m) basement room with 8 foot (2.4 m) ceilings. All four walls and the ceiling get board.
- Walls: 48 ft around x 8 ft high = 384 sq ft
- Ceiling: 12 x 12 = 144 sq ft
- Total: 528 sq ft
- Add 10 percent: 528 x 1.10 = 580.8 sq ft
With 4 by 8 sheets: 580.8 / 32 = 18.15, so order 19 sheets.
With 4 by 12 sheets: two stacked sheets cover each 12 foot wall (8 total), plus three for the ceiling, so 11 sheets, and 12 if you want a spare for a mistake. Here 12 foot sheets waste almost nothing because the room matches the sheet length. A room that is 13 by 14 feet would not work out so neatly.
We did not subtract the door or window. The offcuts and the tricky cuts around them use up the margin.
Most ceilings in this example would be 1/2 inch board. Where framing is 24 inches apart, ask about 5/8 inch or a sag-resistant 1/2 inch board. Walls and ceilings between an attached garage and the house need 5/8 inch Type X fire-rated board where code requires it. The types of drywall post explains which goes where.
How much drywall mud, tape and screws do I need?
These are commonly used planning rules for ordinary walls and ceilings. The label on the pail or roll has the manufacturer's own coverage, and that figure wins.
| Material | Planning rule | For the 528 sq ft room |
|---|---|---|
| Screws | About 1 per sq ft, roughly 32 per 4 by 8 sheet | About 530, so buy 600 |
| Paper tape | About 0.4 to 0.55 ft per sq ft, or 12 to 18 ft per 4 by 8 sheet | About 210 to 290 ft (65 to 90 m) |
| All-purpose compound, Level 4 finish | About 450 sq ft per 17 L (4.5 gal) pail | 1.2 pails, so buy 2 |
| Corner bead | One length per outside corner | Count your outside corners |
How much drywall mud per sheet?
At the 450 square foot rule, one 17 L pail finishes about 14 sheets of 4 by 8, or roughly 1.2 L per sheet, using tape, a fill coat and a finish coat. A Level 5 skim coat over the whole surface takes much more, often more than double. See Level 4 vs Level 5 before you decide how smooth you need it.
How much drywall tape do I need?
Use the table, then round up to a full roll. Paper tape usually comes in 75 m or 150 m rolls (250 or 500 ft). Mesh tape sticks to the board but typically needs more compound, as covered in mesh vs paper tape.
Which screws?
For 1/2 inch board on wood framing, 1 1/4 inch coarse-thread screws are the usual size. For 5/8 inch board, 1 5/8 inch. Steel studs take fine-thread screws. Space them as the manufacturer or building code directs, closer together on ceilings. Also buy sandpaper or sanding sponges, and a second bag of setting-type compound if you want a faster first coat.
Using your numbers to check a drywall quote
Once you know the square footage and sheet count, you have a way to read a quote. Material is the smaller part of a drywall bill. Most of it is the labour to hang, tape, coat, dry and sand, plus hauling and cleanup. That is why a rough drywall cost calculator that only multiplies by square feet will often miss. For typical Ontario price ranges see our drywall cost guide.
When you compare quotes, ask:
- How many square feet does the contractor count, and does it include ceilings, bulkheads and stairwells?
- Which board thickness and type, and where is the moisture-resistant or fire-rated board?
- What finish level, and how many coats of compound?
- Is dust control, delivery, carrying the board in and garbage removal included?
- Is waste built into the sheet count?
If you want a second opinion on a number, D&D Interior Services gives a free written quote for drywall and plastering that lists the measured area and the finish level.
Ordering and storing drywall in Ontario
- Ask about delivery and placement. Some suppliers will carry sheets inside for you. It saves your back and the damaged edges that come from dragging sheets down stairs.
- Store sheets flat. Lean them on edge for a long time and they bow. Keep them off a damp basement floor and away from open doors in humid weather.
- Let cold sheets warm up. Board that sat in a freezing truck or shed in winter should come up to room temperature before you hang it. Follow the manufacturer's instructions.
- Keep the extra sheet. A spare covers a cutting mistake today and a patch later. Ask the supplier about return policy on unopened, undamaged sheets.
- Check permits. Finishing a basement, moving a wall or adding a suite usually needs a permit, so check with your municipality's building department before framing and boarding.
Drywall quantity questions
How much drywall do I need for a 12x12 room?
A 12 by 12 foot room with 8 foot ceilings has about 528 square feet of wall and ceiling. With 10 percent waste that is roughly 581 square feet, or 19 sheets of 4 by 8 board, or 11 to 12 sheets of 4 by 12. Walls only, with no ceiling, come to about 14 sheets of 4 by 8.
How much drywall mud do I need?
A common rule is one 17 L (4.5 gallon) pail of all-purpose compound for every 450 square feet of board, enough for tape, a fill coat and a finish coat to a Level 4 finish. A 528 square foot room needs about 1.2 pails. Buy two, since you will lose some to sanding and mixing. Check the label.
How much drywall tape do I need?
Plan on roughly 0.4 to 0.55 feet of tape for every square foot of board, or 12 to 18 feet per 4 by 8 sheet. For a 12 by 12 room with a ceiling that is 210 to 290 feet. Buy a full roll, since running short stops the job.
Is there a drywall cost calculator I can trust?
A calculator can total the sheets, mud, tape and screws, but it cannot price the labour, which is the bigger part of the bill. Use it to check quantities in a quote. For the final number, ask for a written quote that lists the measured area, the board type and the finish level.
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Get a Free Interior QuoteKey Takeaways
- Sheets = (wall area + ceiling area) x 1.10 / sheet area, rounded up.
- A 4 by 8 sheet is 32 square feet and a 4 by 12 is 48. Check stairs and doorways before ordering long sheets.
- A 12 by 12 basement room with 8 foot walls is about 528 square feet: 19 sheets of 4 by 8, or 11 to 12 of 4 by 12.
- Rules of thumb: one screw per square foot, one 17 L pail of compound per 450 square feet, 0.4 to 0.55 feet of tape per square foot.
- Material is the smaller part of the cost. Compare quotes on measured area, board type and finish level.
Plan your renovation
Select the room or finish you want to change and describe how you use the space.
Prefer to send the details first? Request a quote or call (519) 501-5003.