Drywall calculator: sheets for walls and ceilings

What this calculator does

It calculates the area of the four walls of a rectangular room, subtracts doors and windows, adds the ceiling if you want, and divides by the area of one sheet. Drywall is also called plasterboard, gypsum board or wallboard.

The calculator counts sheets for one layer on one side of the walls. It does not calculate screws, tape, joint compound or framing.

How to use it

1. Choose metric or US units.
2. Enter the length and width of the room and the height of the walls.
3. Choose whether the ceiling is covered as well.
4. Enter the total area of doors and windows, or 0 to ignore them.
5. Enter the width and length of the sheets you plan to buy.
6. Set the allowance for cuts.
7. Select Calculate.

How the result is calculated

1. Wall area = 2 × (length + width) × height − area of doors and windows.
2. Ceiling area = length × width, if the ceiling is included.
3. Area to cover = wall area + ceiling area.
4. Sheets = area to cover × (1 + allowance ÷ 100) ÷ (sheet width × sheet length), rounded up to a whole sheet.

The calculation is by area. It does not plan where each sheet goes, so it cannot tell whether offcuts can be reused. The allowance covers that uncertainty.

Worked example

A room is 4 m long and 3 m wide with walls 2.4 m high. Wall area: 2 × (4 + 3) × 2.4 = 33.6 m². Doors and windows take 3.3 m², which leaves 30.3 m². The ceiling adds 4 × 3 = 12 m², so the area to cover is 42.3 m².

With 10 percent allowance: 42.3 × 1.1 = 46.53 m². One sheet of 1.2 m by 2.4 m covers 2.88 m². Sheets: 46.53 ÷ 2.88 = 16.2, rounded up to 17 sheets.

In US units: a room of 12 ft by 10 ft with 8 ft walls has 352 sq ft of wall. Less 35 sq ft of openings, 317 sq ft remain. The ceiling adds 120 sq ft, which gives 437 sq ft. With 10 percent allowance that is 480.7 sq ft. One sheet of 4 ft by 8 ft covers 32 sq ft, so 480.7 ÷ 32 = 15.02, rounded up to 16 sheets.

About the example values

Sheet sizes depend on the country and the manufacturer. The examples are common sizes that manufacturers list.

The calculator starts with 1.2 m by 2.4 m and 4 ft by 8 ft. Longer sheets mean fewer joints but are heavier and harder to carry into the room.

We did not find a waste percentage published by a drywall manufacturer; the estimating tools of USG and National Gypsum state that their results do not include waste. The 10 percent in the form is an example. Simple rooms with full-height sheets can need less, and rooms with many openings and corners need more.

Common mistakes

• Choosing sheets that are shorter than the wall height when they are hung upright. A horizontal joint across every sheet adds finishing work.
• Forgetting the ceiling when it is part of the job.
• Subtracting every door and window and then running short. Offcuts from openings are often too small to reuse.
• Entering the sheet size in millimetres while the form expects metres. A sheet of 1200 by 2400 mm is 1.2 by 2.4 m.