Skip to content
Trowelly

Drywall Calculator

Enter your room size, doors and windows to see how many drywall sheets to buy for the walls and ceiling.

Units
ft
ft
ft

Each door removes about 21 ft² (3×7 ft).

Each window removes about 15 ft² (3×5 ft).

%
Add prices for a cost estimate (optional)
per sheet

Results

Sheets
15 sheets
Wall area
301 ft²
Ceiling area
120 ft²
Total area incl. extra
463.1 ft²
  • Includes 10% extra. Ceilings usually use ⅝ in or sag-resistant ½ in board.

Where to buy

Quantities from your result, with links to search each store.

Your ZIP code stays on this device. We use it to show stores and suppliers in your area.

You may also need

Links search each store’s website. Check prices and stock before you go.

How to use the drywall calculator

  1. Enter the Room length, Room width and Wall height.
  2. Enter the number of Doors and Windows to subtract.
  3. Under Include the ceiling?, choose walls and ceiling (the default) or walls only.
  4. Choose a Sheet size and set the Extra for cuts (10% by default).
  5. Optionally enter a price per sheet to estimate cost.

How it works

The calculator subtracts about 21 ft² per door (3 × 7 ft) and 15 ft² per window (3 × 5 ft), adds the ceiling if chosen, then adds the extra for cuts.

Sheet areas are 32 ft² for 4 × 8 ft, 40 ft² for 4 × 10 ft and 48 ft² for 4 × 12 ft. The result is the number of full sheets to buy.

Wall area = 2 × (length + width) × height − doors × 21 ft² − windows × 15 ft²

Total area = wall area + ceiling (length × width, if included)

Sheets = total area × (1 + extra %) ÷ sheet area, rounded up

Worked example

With the default inputs, a 12 × 10 ft room with 8 ft walls, one door and two windows has 301 ft² of wall, plus a 120 ft² ceiling, for 421 ft².

With 10% extra that is 463.1 ft². Divided by 32 ft² per 4 × 8 sheet, that is 14.5, so buy 15 sheets. Using 4 × 12 sheets, you would need 10.

Tips before you buy

  • Longer sheets mean fewer seams to tape, but 4 × 12 sheets are heavy. Plan on help, especially for ceilings.
  • Ceilings usually use ⅝ in board or sag-resistant ½ in board.
  • Garages, furnace rooms and walls shared with a garage may need fire-rated board; check your local building code.
  • Use moisture-resistant board in bathrooms, and cement board behind tile in wet areas.

Frequently asked questions

How many sheets of drywall do I need for a 12×10 room?

With 8 ft walls, one door, two windows and the ceiling, the area is 421 ft². With 10% extra that is 15 sheets of 4 × 8 or 10 sheets of 4 × 12.

How many square feet are in a sheet of drywall?

A 4 × 8 sheet covers 32 ft², a 4 × 10 covers 40 ft² and a 4 × 12 covers 48 ft².

Should I subtract doors and windows?

Yes. The calculator removes about 21 ft² per door and 15 ft² per window. Many installers hang board over small openings and cut them out, which the extra allowance helps cover.

What thickness of drywall should I use?

Interior walls usually use ½ in. Ceilings often use ⅝ in or sag-resistant ½ in, and some areas require fire-rated board by code.

How much extra drywall should I buy?

About 10% covers typical cuts and mistakes. Use more for rooms with many openings, angles or short wall sections.

Results are estimates based on the measurements you enter and typical material properties. Products vary, so check quantities with your supplier and follow product labels and your local building codes. Read the full disclaimer. Last reviewed October 9, 2026.