How this calculator works
It measures the four walls as one strip, takes off doors and windows, and adds the ceiling if you include it. The total board area plus a waste allowance is divided by the area of one sheet and rounded up to whole sheets.
Screws, joint compound and tape are estimated from the same board area using common published rates: screws every 16″ on walls and 12″ on ceilings over 16″ framing, about 10 gallons of all-purpose compound and 370 ft of paper tape per 1,000 sq ft.
walls = 2 × (length + width) × height − 21 ft² per door − 15 ft² per window
board area = walls + ceiling (length × width)
sheets = board area × (1 + waste) ÷ sheet area (32 ft² for 4×8, 48 ft² for 4×12)Worked example
A 14′ × 12′ room with 8′ walls has 2 × (14 + 12) × 8 = 416 sq ft of wall. Take off one door (21) and two windows (30) and 365 sq ft is left; the ceiling adds 168, for 533 sq ft of board. With 10% waste that is 586.3 sq ft, or 18.3 sheets of 4×8, so the list buys 19 sheets, 2 boxes of screws (about 554), 2 buckets of compound (5.3 gal) and 1 roll of tape.
Tips before you buy
- Hang ceilings first, then walls, with sheets running horizontally across the framing. Fewer butt joints means less taping.
- Use 4×12 sheets on long walls if you can get them into the room; they cut the number of joints to finish.
- Ceilings over 16″ framing usually take ⅝″ board or ½″ sag-resistant ceiling board, not regular ½″.
- Buy one or two spare sheets for a room with many corners, soffits or openings; off-cuts rarely fit those pieces.
Questions
- How many sheets of drywall do I need for a 12 × 12 room?
- With 8 ft walls a 12 × 12 room has 384 sq ft of wall and 144 sq ft of ceiling. That is 528 sq ft, or 16.5 sheets of 4×8 before you take off openings. With a 10% waste allowance and no openings subtracted, it rounds up to 19 sheets.
- How much waste should I allow for drywall?
- Ten percent is the usual allowance for a simple rectangular room. Use 15% for rooms with many windows, angled walls or soffits, where off-cuts are too small to reuse.
- Should I subtract doors and windows?
- Subtracting standard doors and windows gives a closer count, which is what this calculator does. Many installers hang board over small openings and cut them out afterward, and the waste allowance covers that.
- Is 4×8 or 4×12 drywall better?
- 4×12 sheets cover 48 sq ft each and leave fewer joints, so finishing is faster. They are heavy and hard to carry up stairs or around corners; 4×8 sheets are easier to handle alone.