Craft Quantities
Plan & Takeoffs

Solve backwards

How big a room will my drywall sheets board?

A stack of board finishes less wall than its face area, because every room eats some of it in offcuts. Enter the sheets you have and the net wall they board comes back — the drywall calculator's own waste taken off — with the largest room whose four walls that is.
  • 20 sheetsThe example worked below
  • Drywall CalculatorEvery figure is its own

You have

How much drywall?

sheets

Worked by the Drywall Calculator at the settings below.

Saved amounts stay in this browser.

The settings it uses

Wall Height
8 ft
Number of Doors
1
Number of Windows
2
Area of One Door
21 sq ft
Area of One Window
15.1 sq ft
Waste Factor (%)
10

What it will do

582 sq ft of wall

54.1 m²

  1. One room. Enough for the walls of a room 21 × 18.6 ft with 8 ft walls.

  2. Or several. About 1 room of the size the Drywall Calculator opens on: the walls of a room 13 × 11.5 ft with 8 ft walls.

Check it forwards

Room Length
21 ft
Room Width
18.6 ft
It asks for
20 sheets (4x8 ft)
You have
20 sheets (4x8 ft)

The Drywall Calculator asks for 20 sheets (4x8 ft) at that size, and 21 sheets (4x8 ft) one step larger.

Open this in the Drywall Calculator

If you had more, or less

Around your amount

Each worked by the Drywall Calculator at the same settings.

  1. Half

    10 sheets

    291 sq ft

    the walls of a room 11.3 × 10 ft with 8 ft walls

  2. Yours

    20 sheets

    582 sq ft

    the walls of a room 21 × 18.6 ft with 8 ft walls

  3. Half as much again

    30 sheets

    873 sq ft

    the walls of a room 31 × 27 ft with 8 ft walls

  4. Double

    40 sheets

    1,164 sq ft

    the walls of a room 40 × 36 ft with 8 ft walls

Common amounts

What each amount of drywall covers

The sizes it is usually sold in, each worked by the Drywall Calculator at the settings above.

You haveIt coversAs one roomAverage rooms
10 sheets291 sq ft(27 m²)the walls of a room 11.3 × 10 ft with 8 ft wallsunder 1
20 sheets582 sq ft(54.1 m²)the walls of a room 21 × 18.6 ft with 8 ft walls1
40 sheets1,164 sq ft(108 m²)the walls of a room 40 × 36 ft with 8 ft walls3
60 sheets1,746 sq ft(162 m²)the walls of a room 60 × 53 ft with 8 ft walls5

Twenty sheets are not twenty sheets of wall

The drywall calculator adds ten per cent for cuts, mistakes and irregular walls when it orders, the figure its sources give as standard for a simple rectangular room. Read backwards, the same ten per cent comes off: the stack finishes the wall a tenth smaller than its face area. A room of many corners or a ceiling install wants fifteen.

The sheet is the market's own

A sheet here is the standard board where you are: 4 by 8 feet in North America, 32 square feet or 2.97 m², and 2400 by 1200 mm in metric markets, 2.88 m² or 31 square feet. The two are within three per cent of each other, but a 12-foot board or a short 1800 by 900 board gives a different count — and a different room.

Openings come out before the waste goes on

The room keeps the calculator's door and two windows, and their area is taken off before the waste allowance is added, as if the board cut from a doorway were recovered elsewhere. Reveals returning into each opening still have to be boarded, and a chimney breast or a closet wall adds surface a four-wall room never shows.

How the answer is worked

Nothing here is a second formula. The Drywall Calculator runs forwards — a size in, a quantity out — and this page grows its own starting room in proportion until the quantity it asks for is what you have. Where it rounds up to whole containers, the answer is the largest size before the next one would be needed.

Where the calculator adds an allowance for cuts or breakage when you order, the same allowance comes off here, because it is the same calculator: a stack you already own finishes less than its face value. Where it adds none, neither does this page — the settings beside the answer say which.

Drywall Calculator

runs it forwards

Estimate how many drywall sheets, screws, and how much joint tape you need for a room, based on wall area and a standard waste allowance.

Work out what to buy instead

Solve backwards

Other things you might already have

Solve backwards

Start from what is already in the yard

Paint, sheets, rolls, bags and pieces, each read the other way by the calculator that orders it.

Every Solve Backwards pageDrywall Calculator

  • The calculator's own figures

    Nothing is estimated twice: the page runs the same calculator you would order with.

  • The largest size that fits

    Where a calculator rounds up to whole containers, the answer stops before the next one.

  • Both unit systems

    Gallons and litres, square feet and square metres, side by side.

Frequently asked questions

How much wall does 20 sheets of drywall cover?
At the Drywall Calculator's own settings, 582 sq ft (54.1 m²) — the walls of a room 21 × 18.6 ft with 8 ft walls. That is about 1 room of the size the calculator opens on: the walls of a room 13 × 11.5 ft with 8 ft walls. Every figure follows the settings, which you can change in the calculator.
How many square feet does a sheet of drywall cover?
A standard 4 by 8 foot sheet covers 32 square feet (2.97 m²), and a 2400 by 1200 mm sheet 2.88 m² (31 square feet). After a ten per cent cutting allowance a sheet finishes about 29 square feet (2.6 to 2.7 m²) of wall in a simple room.
How many sheets of drywall does a 12 by 12 room need?
With 8-foot walls, a 12 by 12 foot room has 384 square feet (35.7 m²) of gross wall. Take off one door and two windows and add ten per cent for waste, and the drywall calculator orders 12 sheets of 4 by 8 for the walls — the ceiling is a separate count.
Should drywall sheets hang vertically or horizontally?
Horizontally on most residential walls, because it leaves fewer and shorter joints to tape at a comfortable height; vertically suits walls taller than two sheets or commercial framing codes that require it. The count barely changes, but the joint length — and the tape and compound — does.