How Much Drywall for a 30×40 Room?
A 30 × 40 ft room has 2,320 ft² of wall and ceiling, which needs 80 sheets of drywall with 10% allowed for cuts and waste. Order 80 sheets — use 4 × 12 sheets on long walls to cut the number of butt joints.
Other room sizes
Order 80 sheets — use 4 × 12 sheets on long walls to cut the number of butt joints.
- Wall + ceiling area
- 2,320 ft²
- Waste / cuts 10%
- + 232 ft²
- Coverage to buy
- 2,552 ft²
- Metric
- 215.5 m²
- 4 × 8 ft sheets (32 ft²)
- 80
- 4 × 12 ft sheets (48 ft²)
- 54
- Approx. weight
- 4,320 lb
- Joint compound, 4.5 gal bucket
- 6 buckets
- Paper tape, 250 ft roll
- 4 rolls
- Drywall screws 1¼″, lb
- 8 lb
- Corner bead, 8 ft
- 5 pcs
- Materials + delivery$12–$22 / sheet · Sep 2026
- $1,035 – $1,835
- Installed (with labor)typ. $6,575
- $4,515 – $9,955
- Drywall, ½″ × 4×880 sheets
- Joint compound, 4.5 gal6 buckets
- Paper tape, 250 ft4 rolls
- Drywall screws, 1¼″8 lb
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Different size or depth?
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How to calculate drywall by hand
Area = 2 × (L + W) × H + L × W (ceiling) · Sheets = area × (1 + waste) ÷ 32
Worked example
- Walls: 2 × (12 + 12) × 8 = 384 ft² · Ceiling: 12 × 12 = 144 ft² → 528 ft².
- Waste 10%: 528 × 1.10 = 581 ft².
- Sheets: 581 ÷ 32 = 18.2 → 19 sheets of 4 × 8 (or 13 of 4 × 12).
- Finishing: 2 buckets of compound, 1 roll of tape, 2 lb of screws, 2 corner beads.
- 4 × 8 sheet
- 32 ft² · ½″ = 54 lb
- 4 × 12 sheet
- 48 ft² · ½″ = 82 lb
- Joint compound
- ≈ 1 gal per 100 ft²
- Screws
- ≈ 1 lb per 300 ft² (16″ o.c.)
Questions crews ask
How many sheets of drywall for a 12x12 room?
Walls 2 × (12 + 12) × 8 = 384 ft² plus a 144 ft² ceiling is 528 ft²; with 10% waste, 581 ft² → 19 sheets of 4 × 8 or 13 sheets of 4 × 12. Walls only: 14 sheets of 4 × 8.
Should I subtract doors and windows?
Not for a normal room — the cut-outs come back as waste around the openings. Subtract only large openings such as a garage door or a wall of windows.
How much joint compound do I need?
About 1 gallon per 100 ft² of drywall for three coats (tape, fill, skim) — a 4.5 gallon bucket per 450 ft². All-purpose for taping; lightweight or topping for the finish coats. Add a bucket if you are skim-coating.