Drywall Calculator

Counting sheets is the easy part of a drywall estimate. Divide the net area by the sheet area and round up. What catches people out is everything that follows the joints rather than the area: tape, compound, corner bead and the labour that goes with them.

Sheet size decides how much work follows

A 4 by 12 sheet covers 48 square feet against 32 for a 4 by 8. Fewer sheets is mildly useful. Fewer joints is the real prize, because taping, three coats of compound and sanding take far longer than hanging the board.

Consider a 14 by 12 foot room with 8 foot walls. Sheeted vertically in 8 foot boards, every 4 feet produces a butt joint from floor to ceiling. Sheeted horizontally in 12 foot boards, most walls take two sheets with a single horizontal seam at mid-height and no butt joints at all. Same square footage, roughly half the finishing.

The trade-off is handling. A 4 by 12 sheet of half-inch board weighs about 77 pounds and does not go round a stairwell easily. If you are working alone, 8 foot sheets you can actually lift beat 12 foot sheets you cannot.

Horizontal or vertical

Commercial work is usually vertical, residential usually horizontal. The reason is not aesthetic.

Hanging horizontally puts the long factory-tapered edges together in one continuous seam across the wall, which is the easiest joint to finish invisibly. It also crosses more studs, tying the wall together, and it puts the seam at about waist height where it is easiest to work. Vertical hanging produces butt joints on the untapered ends, which stand slightly proud and need a wider, more careful feather to hide.

Compound: quoted by area, used by joint

Joint compound is estimated per thousand square feet of board rather than per linear foot of seam, because bedding, the second and third coats, and the screw spotting all scale closely enough with area. The working figure is about 140 pounds of ready-mixed compound per 1,000 square feet for a standard three-coat finish, which is roughly 0.053 cubic feet per square foot.

That figure moves with the finish level. The industry standard defines six levels, published jointly by the Gypsum Association and finishing trade bodies:

• Level 1, tape embedded only. Above-ceiling plenum areas nobody sees.
• Level 2, one coat over tape. Garages, behind tile.
• Level 3, two coats. Heavy texture to follow.
• Level 4, three coats. The normal residential standard, suitable for flat paint and light texture.
• Level 5, three coats plus a skim over the whole surface. Required for gloss paint and for walls in raking light, where every joint would otherwise show.

Level 5 uses substantially more compound than Level 4 because the entire surface gets skimmed, not just the joints. If the room has a large window casting light along a wall, or the paint is anything above eggshell, budget for it.

Screws and spacing

The usual pattern is 12 inches apart in the field and 8 inches at edges for walls, tightening to 12 inches everywhere on ceilings because gravity is working against you. That comes out around 32 screws per sheet on walls and closer to 40 on ceilings.

Length follows thickness: 1¼ inch screws for half-inch board on wood framing, 1⅝ for five-eighths. Set them just below the surface without breaking the paper. A screw that tears the face paper has lost most of its holding power and will pop through the finish later.

Which board goes where

Half-inch board is standard for walls. Five-eighths is used on ceilings, where it resists sagging between joists, and is required in many fire-rated assemblies, including the wall between a garage and a house. Check the local code rather than assuming, because that particular requirement is enforced at inspection.

Moisture-resistant board belongs in bathrooms, but not behind a shower or tub surround. Tiled wet areas need cement backer board or a proper waterproof membrane system; the green paper-faced board is not a tile backer and will fail behind one.

Ordering, and what to add

Ten percent waste covers a plain rectangular room. Push to 15 percent where there are many openings, angled walls, or a stairwell, because each cut-out leaves an offcut too small to use elsewhere.

Not counted in the totals above: corner bead for every external corner, at roughly the height of the corner in linear feet, and setting-type compound for the first coat if you are finishing over two days rather than three. Setting compound hardens chemically rather than by drying, so it can be recoated within hours, and it shrinks less than ready-mix on deep fills.