How it works
The formula
board = wall (+ L × W for the ceiling)
sheets = board × (1 + waste) ÷ 32 (4×8) or 48 (4×12), rounded up
Assumptions
- Waste is 10% or 15% on top of the board area, for cutoffs and mistakes. It applies to sheets only, not to compound, tape or screws.
- Joint compound: 0.01 gal per sq ft of board, about 10 gal per 1,000 sq ft, for taping plus a standard three-coat finish. Fine Homebuilding puts it at 11 gal per 1,000 sq ft for premixed compound; USG says about two 4.5 gal pails (9 gal) of its lightweight compound. A bucket is 4.5 gal. Rounded up to whole buckets.
- Paper tape: about 0.37 ft per sq ft of board for the seams (Fine Homebuilding: about 370 ft per 1,000 sq ft), in 500 ft rolls; 250 ft rolls are also common. Buy a spare roll for a room with many corners.
- Screws: 1 per sq ft on walls (16 in apart) and 1.25 per sq ft on the ceiling (12 in apart). Fine Homebuilding figures about 1,000 fasteners per 1,000 sq ft; the ceiling's extra is our allowance for closer spacing. About 215 screws per lb of #6 × 1-5/8 in coarse screws (retailer counts), so a 5 lb box holds about 1,075.
- A standard door takes off 20 sq ft and a window 15 sq ft, the same as in our paint calculator. Doors and windows start at 0 because many people hang full sheets across openings and cut them out.
- Prices are for 1/2 in sheets. Metric: type meters; the room is converted to feet for the math and sheets stay in US sizes.
Worked example
A 12 × 12 ft room, 8 ft walls, ceiling included, 4×8 sheets, 10% waste
- Walls: 2 × (12 + 12) × 8 = 384 sq ft
- Ceiling: 12 × 12 = 144 sq ft, so 528 sq ft of board
- Add 10% waste: 528 × 1.1 = 580.8 sq ft
- Sheets: 580.8 ÷ 32 = 18.15, so hang 19 sheets
- Compound: 528 × 0.01 = 5.28 gal, so 2 buckets
- Tape: 528 × 0.37 = 195 ft, so 1 roll. Screws: about 564, so 1 box
- At the middle of our typical prices: $398.50
Common room sizes, 10% waste
| Room | Walls only | Walls + ceiling | ||
|---|---|---|---|---|
| 4×8 | 4×12 | 4×8 | 4×12 | |
| 10 × 10 ft | 11 | 8 | 15 | 10 |
| 12 × 12 ft | 14 | 9 | 19 | 13 |
| 12 × 14 ft | 15 | 10 | 21 | 14 |
| 15 × 20 ft | 20 | 13 | 30 | 20 |
8 ft walls, no doors or windows deducted, 10% waste. Counts are sheets.
Questions people ask
How many sheets of drywall for a 12x12 room?
With 8 ft walls and 10% waste you need 14 sheets of 4×8 for the walls alone, or 19 with the ceiling. In 4×12 sheets that is 9 for the walls or 13 with the ceiling.
Should I use 4x8 or 4x12 sheets?
4×12 sheets run the whole length of a 12 ft wall, so there is one joint to finish instead of two or three. They weigh about 75 lb each against about 50 lb, and are harder to carry up stairs. For this room the ceiling-included count is 19 sheets of 4×8 or 13 of 4×12. Use the size that fits your walls with the fewest offcuts.
How much joint compound do I need per sheet?
About 0.32 gal for each 4×8 sheet, using 0.01 gal per sq ft. That is roughly 14 sheets per 4.5 gal bucket. Our 19 sheets here need 5.3 gal, so 2 buckets. Rough work or a smooth Level 5 finish uses more.
Do I subtract doors and windows?
Only if you plan to save the cut-out pieces. Many installers hang full sheets across openings and cut them out, which wastes board but saves time. This calculator starts at 0 and lets you enter counts: a door takes off 20 sq ft and a window 15 sq ft. One door and one window in the default room changes 19 sheets to 17.
How many screws per sheet of drywall?
About 32 per 4×8 sheet on walls (16 in apart) and 40 on a ceiling (12 in apart). A 5 lb box holds about 1,075 screws, enough for about 33 wall sheets.
Should I use 10% or 15% waste?
10% suits a plain rectangular room. Use 15% for many corners, angles or short walls. For the default room that is 19 sheets at 10% or 19 at 15%.