How the drywall calculator works
Drywall is sold by the sheet, so the job is to turn your room into a total area and then divide by the area of one board. Here is the whole method:
- Find the wall area. Multiply the room perimeter (2 × length + 2 × width) by the wall height.
- Subtract the openings. Deduct about 21 sq ft for each door and 15 sq ft for each window — you do not board over them.
- Add the ceiling if you are hanging it (length × width).
- Add waste. Ten percent is the working default; more if the room is cut up.
- Divide by the sheet area. A 4 × 8 board covers 32 sq ft. We round up to whole sheets, because you cannot buy part of one.
The calculator also works out the consumables that catch people out at the checkout. Roughly one screw per square foot, one gallon of ready-mixed joint compound per 100 sq ft, and about half a linear foot of joint tape per square foot of board. Those are industry planning figures — enough for embedding the tape plus two or three fill coats — not a substitute for your own experience on a particular job.
Worked example: a 12 × 10 ft bedroom
Here is a full calculation worked through line by line. The room is 12 ft long, 10 ft wide, with an 8 ft ceiling, one door, two windows, and we are hanging the ceiling as well. Standard 4 × 8 sheets, 10% waste.
- Perimeter. 2 × (12 + 10) = 44 ft.
- Gross wall area. 44 × 8 = 352 sq ft.
- Subtract openings. One door at 21 sq ft plus two windows at 15 sq ft each is 51 sq ft. 352 − 51 = 301 sq ft of wall to board.
- Add the ceiling. 12 × 10 = 120 sq ft, so 301 + 120 = 421 sq ft to cover.
- Add 10% waste. 421 × 1.10 = 463 sq ft to buy.
- Divide by the sheet area. 463 ÷ 32 = 14.47, which rounds up to 15 sheets.
The consumables follow from the 421 sq ft you actually install: about 421 screws (roughly 2.5 lb, so buy 3 lb), 4.2 gallons of joint compound (a 3.5-gallon pail plus a one-gallon tub), and around 230 linear feet of joint tape — one 250 ft roll.
The same room without the ceiling
If the ceiling is already finished and you are only doing the walls, drop step four entirely. The area becomes 301 sq ft, with waste that is 331 sq ft, and 331 ÷ 32 = 10.35 — 11 sheets instead of 15. The ceiling is a third of the material on a job this size, which is worth knowing before you order.
The same room in 4 × 12 sheets
Switching to 12 ft boards changes the sheet count more than most people expect. The 463 sq ft to buy divides by 48 instead of 32: 463 ÷ 48 = 9.65, so 10 sheets. That is five fewer boards to carry, and because long sheets span the whole wall horizontally, it removes a full row of vertical seams — meaningfully less taping and sanding. The catch is handling: 12 ft boards weigh over 70 lb in 5/8 inch and need two people plus a clear route from the driveway.
Where the answer moves
- Waste allowance. At 15% instead of 10%, the same room needs 16 sheets rather than 15. Rooms with angled ceilings, Alcoves or lots of small wall segments justify the higher figure.
- Taller walls. A 9 ft ceiling pushes the gross wall area from 352 to 396 sq ft, and the total with waste from 463 to 516 — a jump from 15 sheets to 17.
- Openings. A room with a wide patio door and three windows loses more area to subtraction. The board count goes down, but the cutting gets harder and the waste percentage should go up.
- Boarding only part of a room. For a single wall, use the wall's own length rather than the room perimeter — enter the wall length as the room length and a width near zero.
Change any of these in the calculator and the sheet count, screws, compound and tape all update together. The example is here to show where the numbers come from, not to replace measuring your own room.
Drywall sheet size and thickness reference
Sheet size drives both the board count and the amount of finishing work. Bigger sheets mean fewer seams, and seams are where the labour is.
| Sheet size | Area per sheet | Best for |
|---|---|---|
| 4 × 8 ft | 32 sq ft | The default. Cheapest, easiest for one person, fits through any door |
| 4 × 9 ft | 36 sq ft | Finishing a 9 ft ceiling in one piece with no horizontal seam |
| 4 × 10 ft | 40 sq ft | Common 10 ft walls; one horizontal seam avoided |
| 4 × 12 ft | 48 sq ft | Large open rooms — about a third fewer seams, needs two people |
Thickness is a separate decision, and it is usually set by code or by what the surface has to do.
| Thickness | Typical use |
|---|---|
| 1/4 in | Skim-coating over damaged plaster, curved surfaces, doubling up on existing walls |
| 3/8 in | Repair patches and light remodelling where weight matters |
| 1/2 in | Standard interior walls on studs 16 in on centre |
| 5/8 in | Ceilings (resists sag between joists), Type X fire-rated walls, garage and furnace rooms, sound control |
Moisture-resistant board — the green or purple stuff — is the right call in bathrooms, laundry rooms and basements, where ordinary paper-faced board will feed mould. It costs a few dollars more per sheet and is worth it wherever humidity lingers.
What drywall costs in 2026
Board prices move with lumber and gypsum markets, but these are the ranges most US homeowners are seeing in 2026 for a single 4 × 8 sheet.
| Board type (4 × 8 ft) | Typical price per sheet | Worth knowing |
|---|---|---|
| 1/2 in regular | $13 – $19 | The standard interior wall board; buy by the pallet for a discount |
| 5/8 in regular | $18 – $26 | Heavier and stiffer; the ceiling choice |
| 5/8 in Type X fire-rated | $22 – $32 | Code-required in garages and many shared walls |
| Moisture-resistant (green/purple) | $18 – $28 | Bathrooms, laundry, basements |
| Ultra-light 1/2 in | $18 – $26 | Up to 30% lighter — a real difference when working on ceilings alone |
| 4 × 12 ft, 1/2 in | $25 – $38 | More per sheet but less per square foot and fewer seams |
For the bedroom in the example — 15 sheets of standard 1/2 in board — materials come to roughly $230 to $290: the boards themselves, plus about 3 lb of screws, a 3.5-gallon pail and a one-gallon tub of compound, one roll of tape, corner bead for the outside corners, and consumables like sandpaper and blades. Delivery on a full order usually runs $60 to $120, and it is almost always worth it against hiring a truck and breaking your back.
Hiring the work out splits into two trades, and they are often quoted separately. Hanging typically runs $0.60 to $1.20 per square foot, or around $40 to $60 per sheet. Taping, mudding and sanding runs another $0.50 to $1.50 per square foot depending on the finish level — a smooth Level 5 finish costs more than the standard Level 4 behind texture. All-in installed drywall generally lands somewhere between $1.50 and $3.00 per square foot, which puts the 421 sq ft bedroom between roughly $630 and $1,260 in labour, or about $900 to $1,550 with materials.
Four things move the total more than the price of the board: your region, since labour rates vary by more than double between markets; the finish level you and your taper agree on; ceiling height, because anything much above 9 ft usually carries a surcharge for lifts or scaffolding; and how much demolition and haul-away is needed before the first sheet goes up. Old plaster removal in particular can rival the cost of the new board.
These are planning figures, not quotes. Prices shift with region, season and supplier, and bundled whole-house orders are usually discounted. Use the calculator to get the quantities right, then price the job locally.
Pro tips
- Order a couple of extra sheets. Uncut returns are usually fine, and a mid-job shortage costs a delivery fee plus a day.
- Buy the 3.5-gallon pail of compound for anything bigger than one small room. Per gallon it is dramatically cheaper than one-gallon tubs, and it keeps better once opened.
- Use the longest sheets your access allows. Fewer seams is the single biggest saving in finishing time.
- Plan the layout before you cut. Stagger vertical seams between rows and avoid landing a seam on the corner of a door or window opening, where cracks are most likely.
- Keep the offcuts from the first room. Pieces over about 2 ft are genuinely useful for the next room's short sections.
- Use the share link to save your measurements or send them to a supplier for a quote.