A drywall estimate is surface area divided by sheet area. The surface is the walls, usually the ceiling too, and the sheet is most often 4 ft wide by 8 ft or 12 ft long.
Wall area = 2 × (length + width) × height
Ceiling area = length × width
Sheets = (wall area + ceiling area) × (1 + waste) ÷ sheet area
A 12 × 14 ft room with 8 ft walls
The walls come to 416 sq ft and the ceiling to 168 sq ft, a surface of 584 sq ft. With the planner’s 10% waste allowance the board needed is 642.4 sq ft.
This example assumes
- 4 × 8 ft sheets, 32 sq ft each
- 10% waste allowance, an editable planning default
- Openings not subtracted, so the walls are treated as solid
Worked example 12 × 14 ft room, 8 ft walls, ceiling included
| Material | Calculated | Buy |
|---|---|---|
| Drywall10% waste, 32 sq ft per sheet | 20.08 sheets | 21 × 4 × 8 ft sheets |
| Joint tape370 ft / 1,000 sq ft | 216 ft | 1 × 250 ft roll |
| Joint compound9 gal / 1,000 sq ft | 5.3 gal | 2 × 4.5 gal pails |
| Drywall screws2.7 lb / 1,000 sq ft (planning default) | 1.58 lb | Approx. 1.6 lb |
The sheet calculation is 20.08 sheets, so the list says 21 × 4 × 8 ft sheets. Without the ceiling, the same walls need 15 sheets.
Supporting materials are estimates
Joint tape, joint compound and screws are estimated from published or planning rates per 1,000 sq ft. USG’s estimator, for example, does not include a waste allowance, and the compound figure rests on a USG statement that two 4.5 gal pails finish about 1,000 sq ft. These are labeled estimates in the planner because they vary with the compound, the finish level and how you work.
What changes the estimate?
- Sheet size: 4 × 8, 4 × 10 and 4 × 12 ft change the count and the number of seams
- Whether you include the ceiling
- Whether you deduct large openings, which the planner leaves off by default
- The waste allowance for your cuts
- Tape, compound and screw rates, which are planning defaults
For the measuring side, see how to measure for drywall. For how sheet length changes the count, see 4 × 8 versus 4 × 12 sheets.