Drywall Calculator,
full bill of materials.

Field guide

How to estimate drywall for any room.

Drywall — also called gypsum board, wallboard, or by the brand name Sheetrock — is measured and sold by the sheet. Getting your order right means computing total wall area, subtracting openings, and always adding a waste allowance before you divide by sheet size.

The core formula

For a rectangular room with four walls:

If you're drywalling the ceiling, add:

The gross area fed to the sheet count includes a 10% waste factor — the industry standard for straight cuts on rectangular rooms. Bump it to 15% for rooms with many angles, archways, or first-time installers.

Accounting for doors and windows

Every opening means drywall you don't have to hang, but the off-cuts are rarely reusable. The industry convention is to deduct the opening area from net area (for material calculations like compound and tape) but still run the full gross area through the sheet count, since you'll need those sheets on-site to cut around openings.

This calculator takes a middle approach: openings are deducted from the net area (which drives compound, tape, screws, and primer), but the 10% waste factor on the sheet count absorbs the off-cut waste. Standard opening sizes used:

• Door: 20 sq ft (roughly 3.3 ft × 6.7 ft rough opening — the most common interior pre-hung door)
• Window: 15 sq ft (roughly 3 ft × 5 ft — a standard double-hung window)

For unusually large openings — a sliding glass door, a picture window, a pass-through — measure the actual rough opening and subtract manually before entering dimensions.

Choosing 4×8 vs. 4×12 sheets

Standard 4×8 sheets (32 sq ft) are easier to handle solo and fit in most vehicles. 4×12 sheets (48 sq ft) mean fewer seams on an 8-ft ceiling, which translates to less taping, less compound, and a cleaner finish. On a 9-ft ceiling you'll need to seam either way, so 4×8 is often the practical choice unless you're renting a panel lift.

Why buying screws by the pound is cheaper

Box-store drywall screws sold in small plastic containers (e.g., 100-count boxes) carry a significant per-screw premium — sometimes 3–4× the cost of bulk. The professional move is to buy 1-lb or 5-lb boxes of #6 × 1⅝" coarse-thread screws. A 1-lb box contains roughly 200 screws and costs about the same as a 25-count box in the retail aisle.

The rule of thumb is one screw per square foot of drywall. On a standard 4×8 sheet attached to studs at 16" on-center, that works out to about 32 screws per sheet — one screw per stud, per field row, per 12 inches of height. Edges get screws every 8 inches. Buying in bulk means you'll have leftover screws for repairs, which is always useful.

For thicker ⅝" Type-X drywall (fire-rated), switch to #6 × 2" screws to ensure the required minimum ⅝" penetration into the stud.

Joint compound: coats and quantity

Joint compound (mud) is applied in three stages: the tape coat, the filler coat, and the finish coat. Each successive coat is thinner and wider. The 0.05 gallon-per-sq-ft estimate assumes you're covering flat seams — expect more for inside corners, outside corners with metal bead, and butt joints (the non-tapered edges of sheets that butt together). Pre-mixed all-purpose compound is the most forgiving for DIYers. Lightweight compound shrinks less and sands more easily on finish coats.

Joint compound is sold in 1-gallon, 3.5-gallon (roughly 28 lbs), and 5-gallon (roughly 50 lbs) buckets. Buy at least one size up from the calculator's estimate — opened compound dries out quickly and cannot be sealed back without losing quality.

Paper tape vs. mesh tape

Paper tape (what this calculator estimates) is stronger and flatter than self-adhesive mesh tape, and it's the professional standard for flat seams. It requires embedding in a thin layer of wet compound. Fiberglass mesh tape is easier to apply but creates slightly thicker seams and is better suited for small repairs. On a full-room job, stick to paper tape for butt and tapered joints; use inside-corner bead (paper-faced metal) for 90° corners.

Disclaimer

Quantities are estimates based on standard room geometry. Actual material requirements vary based on ceiling height, number of seams, installer experience, and local building practices. Always verify totals with your materials supplier before purchasing.