Drywall Calculator
Enter room dimensions to get sheet count by size, board weight for delivery planning, joint compound gallons, tape rolls and screw weight — waste included.
Last updated: 2026-09-22
How the calculation works
- Wall area is the room perimeter × height; the ceiling (when included) is length × width.
- Sheet count divides the area by the sheet size and adds the standard 15% waste for cuts around openings and corners.
- Sheet weight uses published figures for 1/2 in standard board (54 lb per 4×8, scaled by size) — the number that matters for whether two people can hang the ceiling.
- Compound and tape follow finishing working averages per 100 ft² of board.
Formula
wall area = 2 × (L + W) × H ceiling = L × W (optional) sheets = ceil(area × 1.15 / sheet_area) weight = sheets × lb_per_sheet mud ≈ 1.5 gal per 100 ft² tape ≈ 0.3 rolls per 100 ft²
| Symbol | Meaning | Unit |
|---|---|---|
A | Total board area (walls + ceiling) | ft² |
1.15 | Waste factor — cuts around openings | — |
54 lb | Weight of a standard 1/2 in 4×8 sheet | lb |
Worked example
Interpreting the result
The sheet count with 15% waste is the order figure — drywall yards sell full units and returns are limited. The weight line is practical: a 4×12 sheet at 81 lb is a two-person lift overhead, which is why 4×8 dominates DIY ceilings. The mud figure covers tape coat plus two finish coats; textured finishes or level-5 finishing add 50–100%. Regular openings (doors, windows) are deliberately not deducted — the waste factor absorbs their cutoffs, and deducting them double-counts the waste allowance.
Assumptions
- Rectangular room, single layer of 1/2 in standard board.
- 15% waste — appropriate for a room with normal openings; long walls with no openings run less.
- Finishing averages: 1.5 gal compound and 0.3 tape rolls per 100 ft² of board.
Limitations
- Not for ceilings over 10 ft, soffits, bulkheads or curved walls — add those areas manually.
- Moisture-resistant and fire-rated (Type X) board weighs 5–15% more than standard.
- No primer/paint quantities — a different takeoff entirely.
Sheet length is a finishing decision
The 4×8 sheet is the default because it handles easily, but professional hangers prefer the longest sheet the walls allow: every butt joint (two sheet ends meeting) is a bump to hide, while tapered edge joints (long edges) feather flat naturally. A 24 ft wall hung with 4×8s has two butt joints; with 4×12s it has one; with 4×16s, none. Each eliminated butt joint is an hour of finishing and a visible flat spot avoided. The trade is handling: a 4×12 sheet weighs 81 lb and needs two people or a drywall lift overhead. On walls, order the longest sheet your clear wall length favors; on ceilings, respect the lift capacity.
Frequently asked questions
How many drywall sheets for a 12×12 room?
Walls: 2 × 24 × 8 = 384 ft²; ceiling 144 ft²; total 528 ft². At 4×8 sheets with 15% waste: 19 sheets. With 4×12 sheets: 13 sheets — fewer joints, faster finishing.
Should I deduct doors and windows?
No — the 15% waste allowance already covers the cutoffs those openings generate. Deducting them and adding waste double-counts and leaves you short on the large sheets that hang between openings.
How much drywall mud per sheet?
About 1.5 gallons per 100 ft² of board covers tape plus two finish coats. A 4×8 sheet is 32 ft², so roughly half a gallon per sheet across a whole job.