How Many Sheets of Drywall Do I Need?

Counting sheets

Four steps, in order.

1. Wall area: the perimeter of the room times the ceiling height. A 12 by 14 room with 8 foot ceilings is 52 x 8, which is 416 square feet.
2. Ceiling area: length times width, 168 square feet in that room.
3. Add 10%: 584 x 1.1, which is 642 square feet.
4. Divide by the sheet: 642 divided by 48 is 13.4, so 14 sheets of 4 by 12.

Do not subtract doors and windows. A door opening is 21 square feet of board you do not hang, but you hang the board over the opening and cut it out afterwards — which is the correct method, because a seam landing on the corner of an opening will crack. Those cut-outs are exactly what the 10% covers.

The drywall calculator does all four steps and draws the sheet layout across an unrolled elevation of the four walls, so you can see where the butt joints land before you buy anything.

Sheet size trade-offs

The seam where two tapered edges meet finishes flat with three passes and almost no sanding. The seam where two square-cut ends meet — a butt joint — has no recess, so the tape and compound sit proud and have to be feathered 16 to 24 inches each side to hide the hump. Every foot of butt joint you avoid is time you do not spend sanding.

Twelve foot sheets are the right answer whenever you can get them into the room. They will not go up a switchback stairwell or through a tight doorway at the end of a narrow hall. Measure that path before you order, because a pallet of 12 foot board that cannot reach the room is an expensive problem.

There is also a thickness decision. Half inch is standard for walls. Five eighths is required on ceilings framed at 24 inches on centre, on garage ceilings under living space, and wherever a fire rating applies. Five eighths also hangs flatter and sounds better, at about 25% more weight per sheet.

Ceilings

Ceilings first, always. The wall sheets then support the ceiling edges and the joint gets a mechanical backup as well as tape.

Use 5/8 inch board on ceilings with framing at 24 inches on centre, and half inch only at 16 inches. Half inch board on 24 inch centres sags between the joists within a couple of years, particularly if there is blown insulation above it adding weight through the humidity cycle.

A ceiling is also where a sheet lift earns its rental fee — about $35 a day. Two people can wrestle a 4 by 8 onto a ceiling; nobody should try it with a 4 by 12 at 82 pounds. Run ceiling sheets perpendicular to the joists so each sheet crosses as many as possible.

Screws, mud, tape

Three consumables, all easy to under-buy.

Screw spacing is 12 inches in the field on walls and 8 inches on ceilings, with framing at 16 inches on centre. Use 1-1/4 inch coarse thread for half inch board over wood, 1-5/8 for five eighths, and fine thread on steel studs. Set each screw just below the paper surface: break the paper and the screw holds nothing, and it will pop out through the finish in the first heating season.

Buy all-purpose compound for the taping coat and lightweight for the second and third. Lightweight sands with a fraction of the effort, and sanding is where the weekend goes. Setting-type compound — the bagged powder that sets chemically — is for filling gaps and for same-day second coats, not for the finish.

Ordering extra

Ten percent covers normal cutting on a rectangular room. Go to 15% when the job has any of these: more than four openings, angled or vaulted ceilings, a stairwell, or anywhere you have to cut around a beam. Those are the situations where a full sheet becomes two unusable offcuts.

Buy the corner bead by counting outside corners rather than by square footage — they bear no relationship. A room with a chimney breast and two returns has six outside corners and would need six lengths of bead from a job that otherwise needs none.

Two specialist boards belong on the order when they apply. Moisture-resistant board goes behind a vanity and around a tub surround, though never as a tile substrate in a wet area. Cement board or a foam board system goes in the shower itself — see the shower tile planning guide for what actually keeps water out of the framing.

Finally, plan the paint at the same time. New board and fresh joint compound are the thirstiest surface in the house, and a drywall primer sealer is what stops the finish coat flashing over every taped seam. Quantities are in how much paint for 1,000 square feet, and whether you need one coat of primer or two is covered in how many coats of paint.