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Project guide

How much plasterboard do I need for a ceiling?

Replacing an old lath and plaster or cracked ceiling starts with the area. Multiply the length by the width, divide by the sheet size and add a little for cuts, then work out the screws and the skim.

Updated Based on manufacturer guidance, sources below

The short answer

Sheets = ceiling length x width / 2.88, plus 10%, rounded up. A 4 x 3.5m ceiling is 14 m², which is 6 sheets of 2400 x 1200mm board, screwed at 230mm centres and skimmed with about 2 bags of Multi-Finish.

The formula

  • Ceiling area (m²) = length x width
  • Sheets = area / 2.88 x 1.1, rounded up (2400 x 1200mm board)
  • Screws = about 15 per m² at 230mm centres on ceilings
  • Skim plaster = area / 10 m² per 25kg bag, plus 10%

Worked example

A 4 x 3.5m bedroom ceiling:

  • Area: 4 x 3.5 = 14 m²
  • Sheets: 14 / 2.88 = 4.9, plus 10% = 5.3, so 6 sheets
  • Screws: 14 x 15 = 210, so 1 box of 500
  • Skim: 14 / 10 x 1.1 = 1.5, so 2 bags

Work it out for your job

Change the measurements and the quantities update straight away.

Length x width of the room.
Leave at 0 if you are only doing the ceiling.
Area to board
14 m²
Boards (+10%)
6 sheets

Your list

  • 612.5mm plasterboard, 2400 x 1200mm
  • 142mm drywall screws, boxes of 1000 (~210 screws)
  • 1Scrim tape, 90m rolls
  • 2Multi-Finish plaster, 25kg bags
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Materials checklist

  • Plasterboard sheets12.5mm board is the usual choice for ceilings on joists at up to 600mm centres.
  • Drywall screws42mm screws for 12.5mm board, at 230mm centres along every joist.
  • Scrim tapeOver every board joint before skimming.
  • Multi-Finish or Board Finish plasterTwo coats to about 2mm. Allow 10 m² per 25kg bag.

You'll also need

  • Noggins between the joists where board edges do not land on timber
  • A board lifter or a second person to hold sheets up
  • Dust masks and eye protection when taking down an old ceiling
  • PVA or a plaster primer if the manufacturer recommends it

Step by step

  1. Check the joistsFind the joist spacing and add noggins so every board edge is supported.
  2. MeasureMultiply the length by the width for the area, then work out the sheets with 10% for cuts.
  3. Fix the boardsRun the long edges across the joists and stagger the end joints. Screw at 230mm centres.
  4. Tape the jointsScrim tape over every joint and round the edges where the ceiling meets the walls.
  5. SkimTwo thin coats of finishing plaster, then a mist coat once it is dry.

Tips from the manufacturers

  • Board the ceiling before the walls so the wall boards support the ceiling edges.
  • Hire a plasterboard lifter for a full ceiling: holding 2400mm sheets overhead is hard work for one person.
  • Older ceilings can contain hazardous materials. If you are unsure what an old ceiling is made of, have it checked before you take it down.

Mistakes to avoid

  • Leaving board edges unsupported between joists, which leads to cracked joints.
  • Using wall screw spacings on a ceiling. Ceilings need closer centres.
  • Forgetting the scrim tape where the ceiling meets the walls.

Frequently asked questions

How many sheets of plasterboard for a 3 x 3m ceiling?

The area is 9 m². 9 / 2.88 = 3.1, plus 10% is 3.4, so 4 sheets of 2400 x 1200mm board.

What thickness of plasterboard for a ceiling?

12.5mm board is the usual choice for joists at up to 600mm centres. Thinner 9.5mm board is only for closer joist spacings.

How many screws per plasterboard sheet on a ceiling?

At 230mm centres, about 15 per m², or about 43 per 2.88 m² sheet.

Can I plasterboard over an old ceiling?

Often, if the old ceiling is sound and you screw through into the joists with longer screws. A sagging or damaged ceiling should come down first.

Sources

Quantities are estimates for typical jobs, using the coverage figures above. Products vary, so check the data sheet for the product you buy, and talk to a professional for structural, electrical or gas work. SmartBuild is independent and not affiliated with any of the manufacturers listed.

How many plasterboards do I need?To work out how many plasterboard sheets you need: each standard 2400 x 1200mm sheet covers 2.88 m². Divide your area by that, add 10% for cuts, then work out the screws, tape and plaster to go with it. How much plaster do I need to skim a wall or room?A finish skim is about 2mm thick. British Gypsum says a 25kg bag of Multi-Finish covers about 10 m² at that thickness. How much paint do I need for new plaster?Fresh plaster is thirsty. It needs a thinned mist coat to seal it before the full coats, so you need more paint than for a repaint. Here is how much, and how to do it.

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