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A plastering estimate, worked the way a plasterer quotes.
This free plastering estimate calculator walks an interior the way you would measure it on site: room by room, the board spec on walls and ceilings, the finish level, the cornice, then the removal, prep and access. It prices each part the way a working plasterer would and folds it into one figure you can read at a glance.
It is built for the plasterer who wants a fast, defensible ballpark before a formal quote, and the owner who wants a real number before the calls start. Your job saves in the browser as you go, so you can step away and pick it back up. In a hurry, Quick Estimate adds a room or a ceiling patch and returns a figure on one screen. Every number here is a guide estimate to plan around, not a fixed quote: a real price still needs eyes on the room.
How to calculate plasterboard for a room
Measure each wall, length × height, add them together, subtract the openings, add the ceiling if you are sheeting it, then divide the total by the coverage of the sheet you are using and add waste. That is the whole method, and it works the same on one bathroom or a whole house.
Measure to the actual ceiling height rather than assuming it. Heights vary between houses, and sometimes between rooms in the same house, and the height drives both the wall area and which sheet length suits.
Count openings only when they are big enough to matter. A full door or a window comes off the total. A power point or a light switch does not, and deducting them costs you more time than it saves in board.
Standard sheet sizes and what each one covers
Australian plasterboard comes 1200mm wide, in a few standard lengths. The length usually follows the ceiling height, because matching the sheet to the wall height is what keeps joins out of the middle of the wall. Longer sheets mean fewer joins to set, so less jointing labour, but they are heavier and harder to get into a tight room.
Coverage is the length times the width:
- 2400 × 1200mm covers 2.88 m²
- 2700 × 1200mm covers 3.24 m²
- 3000 × 1200mm covers 3.6 m²
- 3600 × 1200mm covers 4.32 m²
A worked example
Take a room 3.6m × 3m with 2.7m ceilings, one standard door and one window, sheeting the walls and the ceiling.
- Perimeter: 2 × (3.6 + 3) = 13.2m
- Wall area: 13.2 × 2.7 = 35.64 m²
- Openings: a 2040 × 820mm door is 1.67 m², a 1800 × 1200mm window is 2.16 m², so 3.83 m² comes off
- Net walls: 31.81 m²
- Ceiling: 3.6 × 3 = 10.8 m²
- Total: 42.61 m²
- Add 10% waste: 46.87 m²
- At 3.24 m² a sheet (2700 × 1200): 14.47, so 15 sheets
At 15% waste the same room needs 16 sheets, which is why the waste figure is worth thinking about rather than guessing.
Waste, and what else is in a plastering quote
A rule of thumb is 10 to 15% waste. Square rooms with simple runs sit at the low end. Raked ceilings, bulkheads, curved walls, lots of small rooms and anything with plenty of cuts sit at the high end, because every cut leaves an offcut too small to use.
The board is only part of the job. A quote also covers screws, adhesive, jointing compound and tape, corner bead, the setting coats, sanding, and the labour to hang, set and clean up. Usually the board is the smaller part of the bill and the labour is the bigger part.
Common questions
Is this a real plastering quote?
No, and it does not pretend to be. It gives you a guide estimate to plan around: close enough to budget with, quick enough to get before you commit. A firm quote still needs a plasterer to see the rooms, the access, and the state of what is already there.
How does it work out the price?
It prices the job the way a plasterer does: board area by the square metre for walls and ceilings, adjusted for the board spec and the finish level, plus cornice by the lineal metre, then the removal, prep and access on top. Change an input and the figure moves, so you can see what a higher finish level or ornate cornice adds.
What is a finish level?
It is how smooth the finished surface has to be, and it drives the labour. Level 3 is a fair standard wall, Level 4 is the usual finish under most paint, and Level 5 is the flawless job for gloss or raking light. The higher the level, the more coats and sanding, so the figure climbs with it.
Who is it for?
Plasterers who want a quick, defensible ballpark before they write a formal quote, and owners or builders who want an honest number before the calls start. Same tool, same maths, either way.
What is Quick Estimate mode?
Instead of the full room-by-room walkthrough, Quick Estimate lets you add a room or a ceiling patch, punch in the numbers, and read a price band on one screen. When you want the detailed version, the full walkthrough is one tap away and your figures carry over.
Does it save my progress?
Yes. Your job is kept in your own browser as you work, so you can leave the page and come back to it later. Nothing is sent anywhere unless you choose to email yourself the summary at the end.
How many sheets of plasterboard do I need?
Add up your wall area, take off the doors and windows, add the ceiling if you are sheeting it, add 10 to 15% for waste, then divide by the coverage of your sheet. A 3.6 × 3m room with 2.7m ceilings works out to about 15 sheets of 2700 × 1200.
How much waste should I allow for plasterboard?
A rule of thumb is 10 to 15%. A square room with long, simple runs sits at the low end. Raked ceilings, bulkheads, curved walls and lots of small rooms sit at the high end, because every cut leaves an offcut too small to use.
What size is a standard sheet of plasterboard in Australia?
Sheets are 1200mm wide and come in 2400, 2700, 3000 and 3600mm lengths. That is 2.88, 3.24, 3.6 and 4.32 m² of coverage per sheet. The length usually follows the ceiling height, so the sheet meets the wall height without a join through the middle.