A drywall calculator works out the wall and ceiling area of a room and divides it by 32 square feet, the size of a 4 by 8 sheet. Formula: Wall area = 2 × (length + width) × height; add length × width for the ceiling; sheets = area ÷ 32, rounded up. A 14 by 12 foot room with 8-foot walls has 584 square feet of walls and ceiling, which takes 19 sheets. At $14 a sheet, that is $266.
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How to use the drywall calculator
- Enter the room length and width in feet.
- Enter the wall height. Most rooms are 8 feet; many newer homes have 9-foot walls.
- Choose whether to include the ceiling.
- Enter the price of one 4×8 sheet of the type you plan to use.
The drywall calculator returns the area, the number of sheets and the sheet cost.
What formula does the drywall calculator use?
The wall area is the room’s perimeter, 2 × (length + width), times the wall height. If you include the ceiling, the floor area, length × width, is added. A 4×8 sheet covers 32 square feet, so the sheet count is the area divided by 32, rounded up to a whole sheet.
Doors and windows are not subtracted. That built-in extra covers cut-offs and broken corners in most rooms, which is why many installers do not deduct small openings.
Drywall calculator worked example
Results from the drywall calculator:
| Room | Ceiling | Area | 4×8 sheets | Cost |
|---|---|---|---|---|
| 14 × 12 ft, 8 ft walls, $14 a sheet | Yes | 584 sq ft | 19 | $266.00 |
| 14 × 12 ft, 8 ft walls, $14 a sheet | No | 416 sq ft | 13 | $182.00 |
| 20 × 16 ft, 9 ft walls, $16 a sheet | Yes | 968 sq ft | 31 | $496.00 |
| 10 × 10 ft, 8 ft walls, $13 a sheet | No | 320 sq ft | 10 | $130.00 |
The ceiling adds a lot. In the 14 by 12 foot room it is 168 square feet, six more sheets.
Using 4×12 sheets instead
Larger sheets mean fewer seams to tape. A 4×12 sheet covers 48 square feet, so divide the area from the drywall calculator by 48 instead of 32. For the 584-square-foot room, that is 12.2, or 13 sheets. They are heavy and awkward on ceilings, so many people use them on walls only and hang ceilings with help or a drywall lift.
What else to buy
Sheets are only part of the job. You also need screws, joint tape, joint compound and corner bead for outside corners. Moisture-resistant board is often used in bathrooms, and fire-rated board may be required in some places, such as a wall between a garage and the house. Ask your local building department which rules apply.
If you are removing old walls in a home built before 1978, the EPA warns that many such homes still have lead-based paint, and sanding or demolition can release lead dust.
Planning a whole basement or addition
For a larger project, list every room and closet with its length, width and wall height. Run the drywall calculator for each, choosing walls only for rooms where the ceiling will stay, and add the sheet counts. Then add a few spare sheets for the whole job rather than per room. If ceilings are taller than 8 feet, 9- or 10-foot-long sheets can cut down on seams, so ask your supplier what lengths they stock.
Keep a note of which rooms need moisture-resistant or fire-rated board so you order the right mix.
Common mistakes to avoid
A common mistake is measuring the floor and forgetting closets, which add wall area. Another is using the nominal ceiling height when the walls are taller. A third is buying exactly the count with no spares for damaged pieces. Run the drywall calculator room by room and add the results.
Prices change from store to store and week to week, so price the exact items you plan to buy on the same day, and keep the receipt for anything you might return.
Estimates for planning only. Prices, codes and site conditions vary; get a written quote and check local building rules before you buy materials.
Related converters and calculators
Related calculators:
- Square footage calculator: room area
- Tile calculator: bathroom walls
- BTU calculator: heat the finished room
Sources
EPA: Lead Renovation, Repair and Painting Program.
Questions about this calculator
How many sheets of drywall do I need for a 12x12 room?
With 8-foot walls and the ceiling, the area is 528 square feet, so 16.5, or 17 4×8 sheets.
How much area does a 4×8 sheet of drywall cover?
Thirty-two square feet.
Should I subtract doors and windows?
The drywall calculator does not. The extra usually covers waste from cuts.
Does the drywall calculator include the ceiling?
Only if you choose to include it.
How much does drywall cost per sheet?
It depends on thickness, type and store. Enter the price you are quoted.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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