How it's calculated
The calculator finds the wall area of a rectangular room (and the ceiling, if you include it), adds a waste allowance, and divides by the area of one sheet. Walls and ceiling are counted separately and each is rounded up to whole sheets, because offcuts from one rarely finish the other. USG's submittal sheet for Sheetrock UltraLight panels lists 4 ft wide panels in lengths from 8 to 16 ft USG; the calculator offers 4 × 8, 4 × 10 and 4 × 12 ft, the sizes in USG's screw-usage chart.
Screws come from that chart in USG's Gypsum Construction Handbook, which gives estimated screws per 1,000 sq ft of board by panel size, orientation, framing spacing and screw spacing USG. The calculator uses USG's maximum screw spacing for single-layer board on wood framing: 16 in on walls and 12 in on ceilings.
Joint compound uses USG's coverage for Sheetrock All Purpose ready-mixed compound: approximately 10 gallons per 1,000 sq ft of panels, sold in 4.5 gallon pails USG.
The formula
- Wall area = 2 × (length + width) × wall height − large openings you leave out.
- Ceiling area = length × width (if included).
- Sheets = wall area × (1 + waste %) ÷ sheet area, rounded up, plus the same for the ceiling.
- Screws = (wall area × USG rate at 16 in + ceiling area × USG rate at 12 in) ÷ 1,000 × (1 + waste %). USG notes that an allowance should be made for loss, so the waste percentage is applied here too.
- Joint compound = board area × 10 gallons ÷ 1,000 sq ft. Pails = gallons ÷ 4.5, rounded up.
- Metric: lengths in meters are converted with NIST's exact 1 ft = 0.3048 m, and compound is shown in liters (1 US gallon = 3.785411784 L) NIST.
You can check a chart value by hand. A 4 × 8 sheet hung across studs 16 in apart crosses 7 studs; with screws every 12 in down its 4 ft height, each stud gets 5 screws, so 35 screws hold 32 sq ft of board, which scales to the chart's 1,094 per 1,000 sq ft.
Worked example
A 12 × 14 ft room with 8 ft walls has 584 sq ft of walls and ceiling to cover. With 4 × 8 sheets and a 10% allowance it takes 21 sheets, about 603 screws on 16 in framing, and 5.8 gal of joint compound (2 pails).
| Line | Amount |
|---|---|
| Walls: 15 sheets × $15.00 | $225 |
| Ceiling: 6 sheets × $15.00 | $90 |
| Sheets total | $315 |
Switching to 4 × 12 sheets cuts the count to 14 and means fewer joints to tape, but each sheet is heavier to lift.
Assumptions and limitations
- Waste allowance is a starting point. USG says to allow for loss but gives no percentage; 10% is a common rule of thumb, not a manufacturer figure. Rooms with many corners, soffits, windows or short walls need more.
- Single layer, wood framing. The screw rates are for single-layer board screwed to wood framing at USG's maximum spacing. Steel studs, resilient channel, adhesive or fire-rated assemblies have their own fastening schedules.
- Openings. Leaving small openings in the area gives a little extra board for cutouts. Subtract only large openings such as wide doorways.
- Compound varies by product. The 10 gallons per 1,000 sq ft figure is for USG's all-purpose ready-mixed compound; lightweight, topping and setting compounds differ. Joint tape and corner bead are not included.
- Prices are examples. Enter your own.
Ready to finish the walls? The paint calculator estimates paint for the same room.