Drywall Calculator

How to use this calculator

1. Measure the room. Enter the length, width and wall height, then pick walls, ceiling or both. For an L-shaped room or separate walls, add them up under Total wall length and type in the ceiling area.
2. Subtract openings. Enter the number of doors and windows. A door counts as 20 sq ft (36 × 80 in) and a window as 15 sq ft (3 × 5 ft). You can change these sizes under Garage, ceiling texture, insulation & fasteners.
3. Pick the board. Choose the sheet size, thickness, framing spacing and which way you hang the sheets. Under the extra options, mark a garage, a water-based ceiling texture or insulation resting on the ceiling. If your board doesn’t meet the code for that job, the calculator shows the board you need instead of a shopping list.
4. Set the waste allowance and prices. The prices are examples, so enter your own. An empty price field never counts as $0: the cost shows “Enter price” until every price is filled in.

The formula

Area to cover = wall length × wall height - doors - windows (+ ceiling area)

Sheets = area ÷ sheet area × (1 + waste %), rounded up, walls and ceiling counted separately

A 4 × 8 sheet covers 32 sq ft, a 4 × 10 covers 40 and a 4 × 12 covers 48. All three are standard sizes: USG and Georgia-Pacific list 4 ft wide, 1/2 in board from 8 ft (USG from 6 ft) up to 16 ft long.

If a sheet is longer than the space it covers, such as a 12 ft sheet stood up on an 8 ft wall, only the part that fits counts (32 sq ft). Offcuts like that rarely get reused.

Sheets hung across the framing have to end on a stud or joist. On framing 16 in on center, a 10 ft sheet is counted at 112 in (37.3 sq ft). In the example room below, that means 11 wall sheets and 5 ceiling sheets of 4 × 10. At 24 in on center, and for 8 and 12 ft sheets, nothing gets trimmed.

The 10% waste allowance is a rule of thumb, not a code or manufacturer figure. Raise it for rooms with many corners, soffits, short walls or openings.

Worked example: a 14 × 12 ft bedroom

8 ft walls, one door, two windows, 1/2 in board on studs and joists 16 in on center, 4 × 8 sheets hung across the framing:

• Walls: 2 × (14 + 12) = 52 ft × 8 ft = 416 sq ft - 20 (door) - 30 (windows) = 366 sq ft
• Wall sheets: 366 ÷ 32 = 11.4 × 1.10 = 12.6 → 13 sheets
• Ceiling: 14 × 12 = 168 sq ft ÷ 32 = 5.25 × 1.10 = 5.8 → 6 sheets
• Total: 19 sheets (13 with 4 × 12 sheets: 9 for the walls and 4 for the ceiling)
• Screws: 13 × 28 + 6 × 35 = 574 (see below)
• Joint compound: 534 sq ft × 10 gal per 1,000 sq ft = 5.3 gal → 2 pails of 4.5 gal
• Tape: 534 × 370 ÷ 1,000 = 198 ft → 1 roll of 250 ft
• Cost at the example prices: 19 × $16 + 2 × $22 + $6 = $354

How many screws does drywall need?

The 2024 IRC (Table R702.3.5) sets the maximum framing spacing and fastener spacing for each board thickness when you don’t use adhesive. These are the values the calculator uses:

The screw count comes from those spacings, not from a manufacturer figure. Each sheet gets a line of fasteners on every stud or joist it covers, with one at each edge. A 4 × 8 sheet hung across 16 in framing covers 7 members. On a wall, each 48 in line takes 4 screws at 16 in spacing (28 per sheet). On a ceiling, each line takes 5 at 12 in (35 per sheet). Since these are maximum spacings, buy a few extra.

Screws into wood framing must be Type W or Type S (ASTM C1002) and go at least 5/8 in into the wood (R702.3.5.1). For 1/2 in board, that means screws at least 1 1/8 in long.

Which way should you hang drywall?

On walls, the code lets you hang the board either way, across or along the studs. All edges and ends have to land on framing, except edges that run across it (R702.3.5). That’s why a 10 ft sheet hung across studs 16 in on center gets trimmed (see above) or needs blocking behind its ends. On ceilings, 3/8 in board and any board on joists 24 in on center must run across the joists.

Ceiling texture and insulation (Table R702.3.5, note d). Don’t use 3/8 in board on a ceiling that gets a water-based texture or carries insulation. Under a water-based texture, hand or spray applied, run the board across the joists and use at least 1/2 in board at 16 in on center. At 24 in on center it must be 5/8 in, or 1/2 in sag-resistant ceiling board, which has its own entry in the thickness list.

Drywall in a garage

Under R302.6, the garage has to be separated from the house:

• Walls and ceiling between the garage and the house or attic: at least 1/2 in gypsum board on the garage side.
• Garage ceiling with living space above: at least 5/8 in Type X board, fastened at 6 in with 1 7/8 in galvanized nails or equivalent drywall screws. Walls that support that floor need at least 1/2 in board.

The calculator won’t accept 3/8 in board for a garage. Doors between the garage and the house have their own rules (R302.5). Local jurisdictions adopt and amend the code, so check with your building department before you start.

How much joint compound and tape?

The calculator uses USG’s published coverage for its Sheetrock products: about 10 gallons of ready-mixed all-purpose compound and about 370 ft of paper tape per 1,000 sq ft of board. A skim coat over the whole surface takes more. Corner bead isn’t included, so measure your outside corners separately.

Tips before you buy

• Longer sheets mean fewer end joints, and end joints are the hardest to finish. But long sheets are heavier and harder to get through doors and up stairs. USG lists 1/2 in UltraLight board at about 1.25 lb per sq ft, so a 4 × 12 sheet weighs about 60 lb.
• Keep regular board away from water. Regular gypsum board must not be installed where it is exposed to the weather or to water (R702.3.5). Behind tile in tubs and showers, use a backer listed in R702.4.2. The tile calculator explains which ones.
• Fire-rated assemblies and electrical work go beyond a materials estimate. Follow the manufacturer’s instructions and your building department.

Last reviewed Oct 9, 2026. See how we calculate. Results are planning estimates - confirm with your supplier and local code.