Estimating plasterboard looks simple: area divided by sheet size. But the waste comes from how sheets fit the walls, and the consumables are where many estimates fall short. A complete takeoff covers the board, the fixings, the finishing materials and the beads, and treats ceilings, walls and wet areas separately.
Measure walls and ceilings
Measure the room perimeter and multiply by the wall height. Subtract large openings such as doors, windows and archways, but not small ones: you'll rarely use the offcut from a switch box or a small window. Add the ceiling area if you're boarding it. For sloped ceilings and gable walls, split them into rectangles and triangles.
Standard deductions: about 1.9 m² per door and 1.5 m² per typical window.
Pick the sheet size
In Australia, 10 mm plasterboard is standard on walls and 13 mm on ceilings, in sheets 1200 mm wide from 2400 mm up to 6000 mm long, with 1350 mm wide sheets to suit 2.7 m walls. Long sheets laid horizontally mean fewer butt joints but need two people or a sheet lifter.
Choose the right board
- Standard board for most walls and ceilings.
- Moisture-resistant board in bathrooms and kitchens. Use a proper backer board behind tiles in showers.
- Fire-rated board where required, such as garage-to-house walls and ceilings, and walls between attached dwellings.
- Acoustic board between bedrooms and on walls between attached dwellings.
- Thermal or insulated board on external walls.
List each board type as its own line, because they're priced differently.
Waste
10–12% covers most rooms. Go higher for rooms with lots of short walls, sloped ceilings, stairwells or many openings.
Consumables people forget
- Screws and adhesive: sheets are usually fixed with stud adhesive daubs plus screws at the edges and ends, about 25 screws per sheet.
- Compound: a base coat for taping and first coats, about one 20 kg bag per 30 m² of board, and a topping compound for the finish coats, about one 15 L tub per 40 m².
- Paper tape: about 1.25 m per m² of board, in 75 m rolls.
- External corner bead for every outside corner and window reveal, plus stop bead at edges.
- Adhesive if you're fixing straight to masonry (direct stick).
- Sanding sheets or mesh, primer or mist coat for the decorator.
- Cornice around the ceiling, with cornice adhesive. Cove cornice comes in 4.2 m lengths and is priced by the lineal metre.
Levels of finish
AS/NZS 2589 sets levels of finish for plasterboard, from Level 3 for heavy textures to Level 5, a full skim for critical lighting and gloss paint. Level 4 is the usual standard in homes. Each level adds coats, compound and labour, so agree the level in writing before you price.
A worked example
A 4.2 × 3.6 m room with 2.4 m walls, one door and two windows: walls 32.5 m², ceiling 15.1 m², total 47.6 m². With 12% waste that's 13 sheets of 10 mm 2400 × 1200 for the walls and 6 sheets of 13 mm for the ceiling. Two bags of base coat, two tubs of topping, a roll of tape, a box of screws and 5 lengths of cove cornice.
Labour
Plasterers often price per m² of board or per room, with cornice per lineal metre. Ceilings, stairwells and small rooms such as toilets take longer per m². Allow drying time between coats in your programme: rushing it shows up as cracks and shrinkage.
The plasterboard calculator handles the whole room and the consumables in one pass, and the plastering calculator covers skim, bonding and render.
Checklist before you send the price
- Walls and ceilings measured separately, openings deducted
- Board types listed for wet, fire and acoustic areas
- Waste set for the room shapes
- Screws, finishing materials, tape and beads listed
- Finish level or skim agreed in writing
- Access equipment for ceilings and stairwells
- Waste removal and clean-up
Common questions
Should I hang ceilings or walls first?
Ceilings first. The wall boards then support the ceiling edges, and the joint is easier to finish.
How long before I can paint?
Each coat of compound needs to dry fully, usually overnight, before sanding and the next coat. Then seal it with a plasterboard sealer before painting.
Pricing per room vs per m²
Pricing by area is fair to both sides on big, open jobs. On small rooms, bathrooms and stairwells, the setting-up, cutting and access time doesn't shrink with the area. Many contractors price small rooms as a fixed sum, or add a minimum charge.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the NCC, Australian Standards and your building surveyor or certifier for your project.