Drywall Calculator

Estimate drywall panels, net surface area and total cost from room dimensions.

Metric or imperial room sizes, 13 panel sizes, and 20 currencies.

Updated October 21, 2026

CreatorFrank Zhao

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Overview

Drywall — also sold as sheetrock, plasterboard or gypsum board — is bought by the sheet, not by the square metre. That makes the useful question a shopping question: how many whole sheets will this room take, and what will they cost? The calculator answers it from the room dimensions, deducts the doors and windows you are not boarding, adds the triangular wall pieces a sloped roof leaves above the walls, and divides the result by the sheet you choose.

What comes back

Gross room area — four walls, the ceiling if you include it, and any triangular space under a sloped wall, before openings.
Total doors area and Total windows area — the parts of that surface that will not be covered.
Net room area — the surface you actually board, after the openings.
Number of panels — whole sheets, always rounded up.
Total cost — the sheet count multiplied by the price you pay for one.

The calculator works from either end. Type the room dimensions and the areas follow; type a measured Gross room area and leave the room boxes empty, and the deductions and the sheet count still work. Lengths can be given in centimetres, metres, inches, feet or yards, or as feet and inches together, and the money in any of twenty currencies.

Most people arrive with a tape measure and a room they want to finish: a spare bedroom, a loft conversion, a garage being lined out, or a rental that needs repairing after a bad tenant. On the other side of the same numbers are fitters and small builders checking a quantity before they quote.

How to use this calculator

Five entries decide the answer: the room, the ceiling, the gable triangles, the openings, and the sheet. Everything else on the page is a result.

Measure the room

Enter the length and width of the floor and the height of the walls. Each box carries its own unit menu, so a metric plan and an imperial tape can be mixed without converting anything first.

If the room is under a pitched roof, stop this height where the sloped wall begins — not at the ridge. The triangles above it are entered in the next box instead.

Say whether the ceiling is being boarded

Include ceiling? adds the floor-sized ceiling to the surface. Leave it on for a room you are lining completely, including the ceiling. Turn it off when the ceiling is already finished, or when it is not being replaced — the sheet count then covers the walls and gables only.

Add the triangular gables, if there are any

For a room under a sloped roof, give the number of identical triangles, the base of one of them and its height. Leave all three at zero for a room with vertical walls and a flat ceiling.

Deduct the doors and windows

Enter how many there are and the size of one. The default door and window sizes are ordinary ones, so change them if yours differ. If your openings vary, use the smallest of them for every opening: that deducts slightly less than the real opening area, so the sheet count errs towards one sheet too many rather than one too few.

Choose the sheet you are buying

Pick a size from Select drywall panel size. The choice sets the area of one sheet, which is what turns the net area into a number of sheets. Sizes are listed in both metric and imperial measurements, so it does not matter which system your supplier uses.

Add the price, then read the result

Type the price of one sheet into Cost per panel to get a total. The price is optional: leave it empty and the page still counts sheets.

Net room area is the surface your sheets have to cover. Number of panels is the number of whole sheets that surface takes. The total is those sheets at the price you entered, before tax and delivery.

A first run-through: a 5 m × 4 m room with a 2.5 m ceiling

One door of 200 × 90 cm and two windows of 120 × 90 cm, ceiling included, 1200 × 2400 mm sheets at 12 per sheet.

Gross area, then the two openings

A_{\mathrm{gross}} = 2 \times 2.5 \times (5 + 4) + 5 \times 4 \times 1 + 0

= 65\ \mathrm{m^2}

A_{\mathrm{doors}} = 1 \times 2 \times 0.9 = 1.8\ \mathrm{m^2}

A_{\mathrm{windows}} = 2 \times 1.2 \times 0.9 = 2.16\ \mathrm{m^2}

Net area, sheets and spend

A_{\mathrm{net}} = 65 - 1.8 - 2.16 = 61.04\ \mathrm{m^2}

A_{\mathrm{panel}} = 1.2 \times 2.4 = 2.88\ \mathrm{m^2}

N = \left\lceil \frac{61.04}{2.88} \right\rceil = 22

C = 22 \times 12 = 264

The page shows 65 m² gross, 1.8 m² and 2.16 m² of openings, 61.04 m² net, 22 sheets and a total of 264 in the currency you chose. The 22 is a minimum: see the tips below for the cutting allowance.

Already have a measured area instead of dimensions?

Leave the room boxes empty and type the total surface you measured into Gross room area. The openings are deducted from that number and the sheet count follows, which is the quickest route for an L-shaped room, an alcove or a ceiling that was measured separately. For example, 52.4 m² of surface with one door and two windows at 1200 × 2400 mm sheets leaves 48.44 m² and gives 17 sheets.

How the area is built up

Every result on the page comes from one chain of additions, subtractions and a single division. Nothing is assumed except the area of the sheet you choose.

The four walls, the ceiling and the gables

The wall band is the distance around the room multiplied by its height, which is the same as two walls of each length:

A_{\mathrm{wall}} = 2h\,(L + W)

The ceiling adds the floor area, multiplied by a switch that is 1 when the ceiling is included and 0 when it is not. The triangular pieces under a sloped roof are added on top. Written as one statement:

A_{\mathrm{gross}} = 2h\,(L + W) + L\,W\,c_{\mathrm{ceil}} + A_{\mathrm{slope}}

$L$ and $W$ are the floor length and width, and $h$ is the wall height.
$c_{\mathrm{ceil}}$ is 1 for a ceiling included and 0 for one left out.
$A_{\mathrm{slope}}$ is the gable area described in the next section; it is zero for a room with vertical walls.

The triangular pieces under a sloped wall

Each identical triangle is half of a base times a height, and the number of them multiplies that area:

A_{\mathrm{slope}} = n \times \frac{b\,h_{\mathrm{t}}}{2}

This area is added to the walls, never subtracted: it is extra wall surface that a rectangular room does not have.

The openings

Doors and windows are counted as rectangles, one size per group:

A_{\mathrm{doors}} = N_{\mathrm{d}}\,h_{\mathrm{d}}\,w_{\mathrm{d}}, \qquad A_{\mathrm{windows}} = N_{\mathrm{w}}\,h_{\mathrm{w}}\,w_{\mathrm{w}}

The surface you actually board

The net area is the gross area with those two totals taken away. This is the number to use for anything you buy by area — joint compound, tape, primer or a contractor's quote:

A_{\mathrm{net}} = A_{\mathrm{gross}} - A_{\mathrm{doors}} - A_{\mathrm{windows}}

Whole sheets, and why the count rounds up

Sheets are sold whole, so the net area is divided by the area of one sheet and rounded up to the next whole sheet:

N = \left\lceil \frac{A_{\mathrm{net}}}{A_{\mathrm{panel}}} \right\rceil

In the example above the division gives 21.19 sheets. You cannot buy 0.19 of a sheet, so the answer is 22 — and those 22 sheets are a minimum, because the sum says nothing about how the sheets are cut and laid out.

The total, and the currency it is shown in

The total is the sheet count multiplied by the price of one sheet:

C_{\mathrm{total}} = N \times p

The price is converted at the current exchange rate, so switching the currency menu changes the number on screen but never the arithmetic underneath. The sheet count does not move when the currency changes.

It runs in both directions

Every number in the wall equation can be the one you know rather than the one you want. Fill in a measured gross area alongside a width and a height and the missing length comes back; type a total for the doors and the door count or the door size is worked out instead. The same is true of the gable triangle and of each opening group.

Two results are deliberately one-way. The sheet count comes from a rounded-up division, so there is no honest way back from 22 sheets to the exact area that produced them; and the total is a display of sheets × price, not a budget you can back-solve. Both are shown read-only for that reason. If you type a measured opening area and the count comes back as something like 1.5 doors, that is the reverse direction doing its job — enter the count and the sizes instead when you want whole openings.

Rooms under a sloped roof

A room directly under a pitched roof has walls that stop before the ceiling, and the space between the top of the wall and the ceiling is a triangle. It is real wall surface, so it has to be boarded and counted — but it also means the room cannot be treated as a box.

What to measure for one triangle

Room height — from the floor to the point where the sloped wall starts, not to the ridge.
Base of triangular space — the width of the triangle along the top of the wall, measured horizontally.
Height of triangular space — the vertical distance from the top of the wall up to where the slope meets the ceiling.
Number of triangular spaces — how many identical triangles the room has. Two opposite walls under a simple pitched roof is the usual case.

Two triangles of 3 m base and 1.2 m height add a little over one extra sheet's worth of surface:

A_{\mathrm{slope}} = 2 \times \frac{3 \times 1.2}{2} = 3.6\ \mathrm{m^2}

Do not measure the room height up to the ridge and also add the triangles. The height box means the vertical wall only, and the triangles carry the sloped part. If you have already worked out the whole surface some other way, put that total into Gross room area and leave the room boxes empty instead.

If the triangles in your room are not identical, work out their total area once and type it into Total area under sloped walls. That box is editable, and the rest of the calculation uses whatever total it holds.

Worked examples

Two jobs that take different routes through the same page: a loft room that needs the gable triangles, and a garage where the ceiling is being left alone.

A loft room with sloped walls

The room is 5 m long, 4 m wide and 2.5 m high to the point where the roof slope starts. Two opposite walls each carry a triangle of 3 m base and 1.2 m height. The ceiling is being boarded, there are no openings to deduct, and 1200 × 2400 mm sheets cost 9.50 each.

A_{\mathrm{gross}} = 2 \times 2.5 \times (5 + 4) + 5 \times 4 + 3.6

= 68.6\ \mathrm{m^2}

N = \left\lceil \frac{68.6}{2.88} \right\rceil = 24

C = 24 \times 9.50 = 228

The gables add 3.6 m², which is more than a whole extra sheet, so this room takes 24 sheets rather than the 23 the walls and ceiling alone would suggest. With the usual ten per cent cutting allowance that becomes 27 sheets.

A garage lined out, ceiling left alone

An attached garage is 6 m long, 4 m wide and 2.4 m high. The ceiling will stay as it is, so Include ceiling? is set to No. There are no doors or windows to deduct — the vehicle door is a separate job. The sheets are the long 1200 × 3000 mm size at 15 each.

A_{\mathrm{net}} = 2 \times 2.4 \times (6 + 4) = 48\ \mathrm{m^2}

A_{\mathrm{panel}} = 1.2 \times 3 = 3.6\ \mathrm{m^2}

N = \left\lceil \frac{48}{3.6} \right\rceil = 14

C = 14 \times 15 = 210

The larger sheet matters here: the same 48 m² in 1200 × 2400 mm sheets would take 17 sheets, because each one covers 2.88 m² instead of 3.6 m². Fewer, longer sheets mean fewer joints to tape, but they are heavier to lift and need a second pair of hands.

Choosing a panel size

The menu lists the ordinary metric sizes plus the four imperial sheets sold in the United States. Each entry carries its exact area, because that area — not the sheet's dimensions — is what divides the net area.

What the sizes are good for

600 × 900 mm (0.54 m²) and 600 × 1200 mm (0.72 m²) — small pieces for patching, boxing in pipes, or a bathroom where a full sheet would have to be cut to pieces anyway.
900 × 1800 mm (1.62 m²) and 1200 × 2000 mm (2.4 m²) — a middle size that one person can still handle on a small landing or in a stairwell.
1200 × 2400 mm (2.88 m²) and 1200 × 2600 mm (3.12 m²) — the everyday wall sheet in metric markets. The 2.6 m length suits rooms with higher ceilings.
1200 × 3000 mm (3.6 m²) — covers the most per sheet and gives the fewest joints, at the cost of weight and handling.
4 × 8 ft (2.97 m²), 4 × 9 ft (3.34 m²), 4 × 10 ft (3.72 m²) and 4 × 12 ft (4.46 m²) — the imperial sheets, measured across the face. A 4 × 8 ft sheet covers about 3% more than a 1200 × 2400 mm one, so the two are close but not interchangeable.

Bigger sheets are faster to hang and leave fewer joints to fill, which is why a professional will often choose the longest sheet that will physically fit. Smaller sheets are easier to carry upstairs, easier to cut accurately and less wasteful in a room full of door openings and corners.

The menu describes size only. It does not choose board thickness, and it does not choose moisture-resistant or fire-rated board — those decisions belong to the room and to the requirements that apply where you are building, so confirm them before ordering.

Measuring tips and common mistakes

Add a cutting allowance on top of the count

The sheet count is exact coverage, rounded up. Real jobs lose sheets to cut-outs, mistakes and damage, so add about ten per cent: 22 sheets becomes 25, and 24 becomes 27. Rooms with many corners or diagonal runs need more.

Keep one spare sheet from the same batch if you can. Colour and surface finish vary slightly between production runs, and a later repair from a different batch can stand out.

Use the smallest opening when they differ

The page takes one door size and one window size. If your windows are different, measure the smallest and enter that size for all of them, keeping the true count. It deducts slightly less than the real opening area, which leaves a little in hand instead of a sheet short.

Measure the height at both ends

Floors and ceilings are rarely perfectly parallel, and a wall can be two or three centimetres taller at one end. Measure at both ends and use the larger figure for a purchase estimate, so the sheets you buy can be trimmed down rather than falling short.

The count ignores the layout

Area is area: 61 m² of net surface is 22 sheets whether they are hung vertically, horizontally or in a pattern. Real rooms are less obliging. A long sheet on a short wall leaves an offcut that may not fit anywhere else, so plan the layout before you order — and treat the sheet count as a minimum rather than a guarantee.

For an L-shaped room, an alcove or a room with a boxed-in pipe, split the wall into rectangles, work out each one with thesquare footage calculatorand add the areas together. That total can then go straight into Gross room area, with the room dimensions left empty.

Questions that come up

Does the calculator include sheets for waste and offcuts?

No. The count is the coverage the room needs, rounded up to whole sheets, and nothing else. Add your own allowance on top — ten per cent is the usual starting point — and go higher for a room with lots of openings, angles or diagonal runs.

Why did the number of doors change to 1.5 when I typed a door area?

Because the page solves in both directions. Once you give it a total door area, the door count and the door size are both free, so it works out whichever one keeps the numbers consistent. A total of 2.7 m² with a 2 m × 0.9 m door becomes 1.5 doors:

N_{\mathrm{d}} = \frac{2.7}{2 \times 0.9} = 1.5

A fractional count is arithmetically right but not something you can buy. If you know how many doors there are, enter the count and the size and leave the total area box empty; clear it and the count becomes an input again.

My ceiling is not the same size as the floor. What now?

The ceiling switch assumes a flat ceiling with the same area as the floor, which covers ordinary rooms but not a vaulted, coffered or partly sloped ceiling. Turn Include ceiling? off, let the page work out the walls and any gables, then add the ceiling area you measured to the net area yourself. The extra surface usually means another sheet or two, so work it out before you order.

Can I mix two panel sizes in one room?

Not in a single run: the sheet count uses one size for the whole room. Choose the size you plan to use most, or run the calculation twice — once per sheet size — and add the counts. That is also the honest way to price a job where you intend to use small pieces around the openings.

Limitations and assumptions

Coverage, not a cutting plan. The sheet count is area divided by sheet area and rounded up. It does not know how the sheets will be laid out, how many offcuts will be unusable, or whether the last sheet is a 100 mm strip.
No waste allowance. Nothing is added for cut-outs, breakage or offcuts. Add your own margin before you buy; see the tips above.
Flat ceiling equal to the floor. Anything else — a vaulted ceiling, a lowered bulkhead, a ceiling that is larger than the floor — has to be added by hand.
One door size and one window size. Mixed sizes are handled by applying one measurement to every opening. Use the smallest if they differ, which deducts a little less than the real area, or work out the true total opening area yourself.
Board type and thickness are outside the calculation. The menu chooses a sheet size, not a board specification. Moisture-resistant boards in kitchens and bathrooms, fire-rated assemblies and the thicknesses required for ceilings are set by the room and by the rules that apply where you build.
Rectangular rooms only. For an L-shaped room, split it into rectangles and add the areas, or enter a measured total surface directly.
Not a structural, acoustic or fire design. Framing, insulation, vapour control, board fixing schedules and fire-rated wall build-ups are not assessed here. For commercial work, fire-rated walls or any structural change, confirm the specification with a qualified contractor or building control.
Prices are a reference figure. One price per sheet, converted at a reference exchange rate, before tax, delivery and any trade discount. Your supplier quote is the number that pays the bill.

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