Drywall calculator
Work out how many sheets of drywall a room or a whole house needs, for whole walls and ceilings or for a flood cut after water damage.
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Your rooms
How the number of sheets is worked out
The wall area of a room is its perimeter (twice the length plus twice the width) times the ceiling height. Doors and windows are taken off: a standard 3' × 6'8" door is about 20 sq ft and a 3' × 4' window about 12 sq ft. Tick the ceiling and its area (length times width) is added.
A 10% allowance is added for offcuts around openings, corners and the ends of walls, then the total is divided by the area of one sheet (32 sq ft for 4' × 8', 40 for 4' × 10', 48 for 4' × 12') and rounded up to whole sheets.
For a flood cut, only the bottom of the walls is replaced: the perimeter times the cut height, less the width of each doorway. Windows are assumed to sit above the cut and the ceiling is left out. Cuts at 2' or 4' use half or a whole sheet's width, so the new pieces come from full sheets with little waste.
These are the same waste allowance and sheet sizes the vPlan AR assistant uses when you ask it how much drywall a scanned or drawn room needs.
Tips
- Longer sheets mean fewer butt joints to tape: 12' sheets suit long walls if you can get them into the room.
- Use moisture-resistant board in bathrooms and laundry rooms, and check what your local code asks for behind tubs and showers.
- For water damage, set the flood-cut height from your moisture readings, not just the visible stain: water wicks up drywall above the line you can see.
- Order tape, joint compound and screws with the board: they are bought by the area hung.
Do this from a scan instead
Scan the room or draw it, then ask the assistant in the web editor how much drywall the rooms need: it measures each wall face inside the room, takes off the real doors, windows and openings, and answers in sheets. On Pro, the Measurement Sheets list every room's net wall and ceiling area in Excel or CSV, ready for an estimate or a claim.
Frequently asked questions
How many sheets of drywall do I need for a 12×12 room?
With 8' ceilings, one door and one window, the walls are 384 sq ft less about 32 sq ft of openings, so about 352 sq ft. Add the 144 sq ft ceiling and 10% waste and that is about 546 sq ft: 18 sheets of 4' × 8', or 12 sheets of 4' × 12'.
How much extra drywall should I buy?
About 10% for cuts around doors, windows and corners. Rooms with many openings, angled walls or short wall sections can need more.
How do I calculate drywall for a flood cut?
Multiply the length of the affected walls by the cut height (usually 2' or 4'), take off each doorway, add the waste allowance and divide by the sheet area. Choose "Flood cut" in the calculator and it does this for every room.
Should I subtract doors and windows from drywall?
Yes, for the sheet count. A standard door is about 20 sq ft and a window about 12 sq ft. Some estimators leave small windows in to cover waste; the calculator takes them off and adds the waste allowance separately.
What size drywall sheet should I use?
4' × 8' sheets are the easiest to carry and fit through doors. 4' × 10' and 4' × 12' sheets cover more with fewer joints, which saves taping time on long walls and ceilings.
Guides
- How to Create a Water Damage Scope-of-Work Report from a Phone ScanScan the affected rooms, tag the damage, and export a professional scope-of-work report — with floor plan, room-by-room condition schedule, and photos — straight from your iPhone.
- How to Work Out Flooring, Paint and Baseboard Quantities from a Floor PlanFlooring needs waste for its pattern, paint needs the doors and windows taken off each wall, and baseboard stops at every doorway. Here is how to work out all three from a floor plan, by hand and in vPlan AR.
- How to Generate a Repair Cost Estimate from a Floor Plan ScanTurn a LiDAR scan into a material takeoff and a line-item cost estimate. Tag the affected materials, apply your own unit prices, and export to PDF or CSV.