Tile area, tile counts and boxes for shower walls and floors.
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Drywall Calculator
InteriorQuick answer: measure the room once and get exact sheet counts for all three common sheet sizes — plus the openings subtracted properly. A 12×12 ft room with 8 ft ceilings, one door and two windows needs 477 ft² of drywall — 17 sheets of 4×8 (or 11 sheets of 4×12) with a 10% waste allowance.
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Sheets 4×8 ft
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Sheets 4×10 ft
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Sheets 4×12 ft
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Net area (ft²)
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Est. cost (4×8 sheets)
Net area subtracts a standard 21 ft² per door and 15 ft² per window. Sheet counts include your waste allowance and are rounded up — offcuts rarely tile a room perfectly.
How it works — the formula
Wall area = 2 × (Length + Width) × Ceiling height · Ceiling area = Length × Width Net area = Walls + Ceiling − (Doors × 21 ft²) − (Windows × 15 ft²) Sheets = ⌈ Net area × (1 + waste %) ÷ Sheet area ⌉ (4×8 = 32 ft², 4×10 = 40 ft², 4×12 = 48 ft²)Bigger sheets mean fewer seams to tape and finish — the slowest part of drywall — but a 4×12 sheet is heavy and awkward in a finished house. Many DIYers hang 4×12 on ceilings with a rented lift and 4×8 everywhere else. Budget roughly one pound of screws per 250 ft² and one 4.5-gallon bucket of joint compound per 350–400 ft² on top of the sheet count.
Worked examples
| Room | Net area | 4×8 sheets | 4×12 sheets |
|---|---|---|---|
| 12 × 12 ft, 8 ft ceiling, ceiling in, 1 door, 2 windows, 10% waste | 477 ft² | 17 | 11 |
| 10 × 10 ft, 8 ft ceiling, walls only, 1 door, no waste | 299 ft² | 10 | 7 |
| 15 × 20 ft, 9 ft ceiling, ceiling in, 2 doors, 4 windows, 10% waste | 828 ft² | 29 | 19 |
Check the first row: walls = 2 × (12+12) × 8 = 384 ft², ceiling = 144 ft², total 528. Openings: 21 + 2×15 = 51. Net 477 ft². With 10% waste: 524.7 ÷ 32 = 16.4, rounded up to 17 sheets.
Frequently asked questions
How many sheets of drywall do I need for a 12x12 room?
528 ft² of surface at 8 ft ceilings with the ceiling in; minus ≈51 ft² of openings, plus 10% waste → 17 × 4×8 or 11 × 4×12.
Should I use 4x8 or 4x12 sheets?
4×12 = fewer seams, faster finishing, but ≈80 lb a sheet. 4×8 is the DIY default; 4×12 pays off with wide access or a ceiling lift.
How much waste should I allow?
10% for a plain rectangular room; 15% with angles, soffits or many short runs.
Do I subtract doors and windows?
Yes — ≈21 ft² per door, ≈15 ft² per average window. Hang over the opening and cut out after; just don't buy board for it.
How many screws and how much mud?
≈1 lb of screws per 250 ft², one 4.5-gal bucket of compound per 350–400 ft², ≈150 ft of tape per 500 ft².
Related tools
Ready-mix yards for the slab under the room.
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Board feet and lumber cost for framing and trim.
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Size the heater or AC for the room you just drywalled.
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See the full list on the Home & DIY Calculators page.
Estimates only. Sheet counts are planning figures based on standard opening sizes; measure unusual openings directly. Follow local code for drywall thickness, fire-rated assemblies and fastening schedules.