Drywall Calculator
Enter the room size and openings to get the number of drywall sheets to buy.
What this tool does
Add the wall area (perimeter × height) and the ceiling area, subtract doors and windows, add about 10% for waste, and divide by the area of a sheet. A 12 × 12 ft room with 8 ft walls, a ceiling, one door and one window needs 17 sheets of 4 × 8 ft board.
Calculates the area of walls and ceiling, deducts openings and adds waste.
Rounds up to whole sheets of the size you choose.
How to use it
- Enter the room length, width and ceiling height.
- Choose whether to include the ceiling.
- Enter the number of doors and windows and the sheet size.
- Read the sheets to buy.
Why use this calculator
Counts the sheets of drywall for a room from its length, width and height, with an option for the ceiling and deductions for doors and windows. Drywall is sold in large sheets that are hard to return, and a shortage mid-job holds up work. A quick area count with a waste allowance gives a safe order.
Why we built it
We built the drywall calculator to include the ceiling, deduct doors and windows and add a waste allowance, then round up to whole sheets. Cover the finished walls with the paint calculator or the wallpaper calculator.
If your task goes further, try the Deck Calculator.
Handy alongside this: the Brick Calculator.
Who this tool is for
- DIYers finishing a room
- Builders estimating sheets
- Landlords refurbishing a flat
When to use it
- Finishing a basement, garage or addition.
- Replacing damaged walls or ceilings.
- Budgeting a renovation.
- Comparing sheet sizes.
How it works
Wall area = 2 × (length + width) × height. Ceiling area = length × width. Doors are taken as 21 sq ft and windows as 15 sq ft and subtracted. Sheets = (area × (1 + waste)) ÷ sheet area, rounded up.
Example: 12 × 12 ft, 8 ft high: walls 384 + ceiling 144 − door 21 − window 15 = 492 sq ft. With 10% waste, 541 sq ft ÷ 32 = 16.9, so 17 sheets.
Taller sheets (4 × 12) mean fewer joints but are heavier to handle. Joint compound, tape and screws are bought separately.
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| Room length | 12 |
| Room width | 12 |
| Ceiling height | 8 |
| Include the ceiling | Yes |
| Doors | 1 |
| Windows | 1 |
| Sheet size | 4 ft × 8 ft (32 sq ft) |
| Waste allowance | 10 |
With those inputs, the calculator returns:
- Sheets of drywall: 17
- Wall area: 384 sq ft
- Ceiling area: 144 sq ft
- Openings deducted: 36 sq ft
- Area to cover: 492 sq ft
- Area with waste: 541 sq ft
What you give it, and what you get back
| Item | Details |
|---|---|
| Room length, width, height | In feet. |
| Ceiling | Include or not. |
| Doors and windows | Counts; standard sizes are assumed. |
| Sheet size and waste | 4×8, 4×9 or 4×12 ft and a waste percentage. |
| Output | Sheets, wall area, ceiling area, deductions and area with waste. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Openings are larger than standard | Doors and windows use standard areas. | Increase the count or reduce the room size by hand. |
| Several rooms | The calculator is for one room. | Calculate each and add them. |
| Slanted ceilings | Not modelled. | Measure the area by hand. |
Assumptions and limitations
- One rectangular room.
- No allowance for second layers or fire-rated boards.
Frequently asked questions
How many sheets of drywall do I need?
Divide the total surface area, with 10% extra, by the area of one sheet.
What size drywall sheet should I use?
4 × 8 ft is the easiest to handle; 4 × 12 ft reduces joints on long walls.
How much waste should I allow?
About 10% for a simple room, more for many cuts.
Do I deduct windows and doors?
Yes for large openings; small ones are usually left in to cover waste.
Is drywall the same as plasterboard?
Yes. Drywall, plasterboard, sheetrock and gypsum board are the same product with regional names.
Is my information sent anywhere?
No. The calculation runs in your browser and nothing leaves the page.
Sources and accuracy
Sheet counts are derived from the net wall and ceiling area using standard gypsum board panel sizes such as 4 by 8, 4 by 9 and 4 by 12 feet, plus a waste allowance. Panel sizes and hanging practice follow industry guidance from the Gypsum Association.
Figures last checked against the source on . Standards and rates can change — if you are relying on this for something that matters, confirm against the source above. Think a figure is wrong or out of date? Send a correction.