Drywall Calculator
Enter your room size and choose a sheet size to find out how many boards you need.
Your measurements
See how we calculated this
Check your order
Your wall and ceiling order
- Measure each surface and opening; check thickness and product coverage.
- Confirm sheet or pack sizes, cuts and the required fixing or finishing system.
- List corners, joints and finishing materials separately from the main surface quantity.
Tools for this job
Measure board cuts before scoring the face paper. Follow the board maker's cutting method, particularly for specialist or cement-based boards.
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- Score and trim suitable sheet materials
Utility knife
STANLEY Classic 99 retractable utility knives
For scoring or trimming sheet materials that allow knife cutting. Choose a blade suited to the material and support the work on a cutting surface.
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Short tape measure
STANLEY 25-foot tape measure
For checking lengths, widths and short runs before ordering. This is a 25-foot tape; use matching units in the calculator and check the scale on the selected model.
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How many sheets of drywall do I need?
Work out the area to be boarded, add a cutting allowance, divide by the area of one sheet and round up. For a room, the wall area is the perimeter multiplied by the height: 2 × (length + width) × height. Add length × width if you are boarding the ceiling as well. Then take off the doors and windows, which this calculator counts at 1.9 m² and 1.5 m² each.
The rounding is where most estimates go wrong. A wall needing 15.9 sheets takes 16 sheets, and a room with short returns, a sloping ceiling or a window in every wall uses far more offcuts than a plain box. That is what the waste allowance covers: 15% is the usual trade figure for a normal room, 10% for plain walls, and 20% where nearly every board gets cut.
The formula
Standard sheet sizes
Thickness does not change the count, but it changes the weight. Manufacturer data sheets put 12.5 mm (1/2 in) standard board at roughly 8 to 9 kg per m², so a 1200 × 2400 sheet is about 25 kg (55 lb) and needs two people on a ceiling. Moisture-resistant, fire-rated and acoustic boards are heavier again.
| Sheet | Area | Where it is used |
|---|---|---|
| 1200 × 2400 mm | 2.88 m² | The standard UK and European board for 2.4 m walls |
| 1200 × 2700 mm | 3.24 m² | Taller rooms; no horizontal joint up to 2.7 m |
| 900 × 1800 mm | 1.62 m² | Lighter to carry upstairs and into lofts; more joints |
| 4 × 8 ft (1219 × 2438 mm) | 2.97 m² (32 sq ft) | The standard US and Canadian sheet |
| 4 × 12 ft (1219 × 3658 mm) | 4.46 m² (48 sq ft) | Long walls and ceilings, fewer butt joints |
Worked example
A bedroom 5 m × 4 m with 2.4 m walls, one door and one window, boarded in 1200 × 2400 mm sheets with a 15% waste allowance.
Perimeter = 2 × (5 + 4) = 18 m. Wall area = 18 × 2.4 = 43.2 m². Deduct 1.9 m² for the door and 1.5 m² for the window = 39.8 m². Add 15% = 45.77 m². Divide by 2.88 m² per sheet = 15.89, rounded up to 16 sheets, which is 46.08 m² of board.
Fixings at 400 mm centres and 300 mm spacing: 46.08 ÷ (0.4 × 0.3) = 384 screws, plus 10% = 423 screws, so a box of 500. Tape: 16 sheets × 7.2 m perimeter ÷ 2 = 57.6 m, one 90 m roll. Compound at 0.4 kg per m² × 39.8 m² = 15.9 kg, which is a 20 kg tub or bag.
What else the job needs
- Drywall screws: 32 mm for 12.5 mm board on timber, 38 mm for 15 mm board or a double layer, and self-drilling screws for metal studs. Ceilings are fixed at closer spacing, so set the spacing field to 230 mm for a ceiling.
- Joint tape: paper tape or self-adhesive fibreglass scrim, usually in 90 m rolls. Paper tape is stronger on internal corners; scrim is quicker on flat joints.
- Joint compound: ready-mixed in tubs for the finishing coats, or a setting powder for the first fill. Both are quoted by weight, which is why this calculator gives kilograms.
- Corner bead for every external corner, sold in 2.4 and 3 m lengths, plus a tub of filler for screw heads.
- If you are building the wall as well, use the insulation calculator for the batts that go between the studs before the boards go on.
- For the finish, either skim the boards with about 2.5 kg of finish plaster per m², or tape and joint them and go straight to the primer calculator and the paint calculator for the decorating.
Measuring and the mistakes that cost a sheet
- Measure wall height floor to ceiling. If it is over 2.4 m, price 2700 mm boards: a horizontal joint on every wall costs more in tape and compound than the longer sheets cost extra.
- Do not deduct small windows or the space behind a radiator. The offcut is rarely the right shape to use elsewhere, and the allowance is already tight.
- Ceilings are boarded first, then walls, so the wall boards support the ceiling edge. Count them together and order once.
- Boards are laid with the long edge across the studs on walls and across the joists on ceilings wherever possible, so that the tapered edges meet on a stud.
- Order on a pallet if you can. Sheets carried one at a time round a tight stair get corner damage, which is where the 900 × 1800 size earns its keep.
Sources and assumptions
Sheet counts divide the wall or ceiling area by the selected sheet area and add waste. Screw, tape and compound figures are approximate quantities, based on the selected support and fixing spacing.
- British Gypsum: GypWall Single Frame A206033 specification: This example system specifies its own stud spacing, board layers, screws, edge distances and support for horizontal joints.
Before using this estimate
- Sheet-area arithmetic does not lay out each wall, doorway, cut edge or horizontal joint. A board layout may need extra sheets or supports.
- The result does not establish fire resistance, sound performance or a suitable ceiling fixing schedule. Use the complete specification for the chosen wall or ceiling system.
Source notes reviewed . See how we check calculations and handle corrections.
Planning your order
Check the inputs before buying: measure the surfaces you need, then apply an allowance and round to whole packs. The guides include worked examples you can follow alongside this calculator.
Published by OrderEnough. This is a planning estimate: check the product specification and the assumptions above before ordering. Last updated . Read how we source our figures on the methodology page.