How to measure a room for drywall
Measure the length and width of the room along the floor and the height from the floor to the ceiling joists. For a room with more than four walls, add all the wall lengths together and enter half of the total as the length and half as the width; the calculator only uses the distance around the room.
The calculator subtracts 21 square feet for each door and 15 square feet for each window. Many drywall hangers run sheets right across small windows and cut the opening out afterwards, so if you have only a couple of small windows you can leave them at zero for a little extra margin.
How the calculation works
Wall area = 2 × (length + width) × height − (doors × 21) − (windows × 15)
Total area = wall area + ceiling (length × width), if included
Sheets = total area × (1 + waste %) ÷ sheet area, rounded up
Screws ≈ one per square foot of drywall hung
In the example above, a 12 × 14 ft room with 8 ft walls has 416 square feet of wall. Removing one door and two windows leaves 365 square feet, and the ceiling adds 168, for a total of 533 square feet. With 10% extra that is 586 square feet, which takes 19 sheets of 4 × 8 ft drywall.
Which sheet size should you use?
- 4 × 8 ft sheets are the easiest to carry, fit in most vehicles and can be hung by one person on walls.
- 4 × 12 ft sheets mean fewer joints to tape and finish, which saves time and gives a smoother wall, but they are heavy and usually need two people.
- On 8 ft walls, many installers hang sheets horizontally, so two 4 ft sheets stacked cover the full height with one seam.
Which thickness and type?
- 1/2 inch is the standard thickness for interior walls.
- 5/8 inch is often used on ceilings because it sags less between joists. Fire-rated (Type X) 5/8 inch board is required in some places, such as certain garage walls and ceilings, so check your local building code.
- Moisture-resistant board is a good choice for bathrooms and laundry rooms. Inside a tiled shower, use a cement board or another tile backer instead of drywall.
Screws, tape and joint compound
A common rule of thumb is about one drywall screw per square foot, which works out to roughly 32 screws for a 4 × 8 sheet. The exact spacing depends on whether you are hanging walls or ceilings and on your local code. Joint tape and compound depend on the number of seams and how many coats you apply, so ask your supplier for an estimate once you know how many sheets you are buying.
Frequently asked questions
How many sheets of drywall do I need for a 12 × 12 room?
The walls of a 12 × 12 ft room with 8 ft ceilings cover 384 square feet. With 10% extra and no openings subtracted, that is 14 sheets of 4 × 8 drywall. The ceiling adds 144 square feet, or about 5 more sheets.
How much waste should I add for drywall?
About 10% for a simple rectangular room and 15% for rooms with many corners, angled ceilings or lots of openings.
How many square feet is a sheet of drywall?
A 4 × 8 sheet covers 32 square feet, a 4 × 10 sheet covers 40 and a 4 × 12 sheet covers 48.
Should I subtract windows and doors?
Subtract doors and large windows. Small windows are often covered and cut out later, and the offcuts are rarely big enough to reuse, so leaving them in the count gives you a useful margin.
This calculator gives an estimate for buying materials. Follow your local building code for fire-rated assemblies and fastener spacing.