Drywall calculator
Sheets, screws, tape and jointing compound for a room — with the compound quantity set by the finish level you are actually going for, not a single average figure.
How this calculator works
Finish level drives the compound, and nothing else does
Board and screws are easy arithmetic. Jointing compound is where estimates go wrong, because the quantity has almost nothing to do with the room and everything to do with how flat you need the wall to be. The industry describes this as a finish level, and the difference between the levels is roughly double:
| Level | kg per m² | What it is |
|---|---|---|
| Level 3 | 0.45 | Tape plus two coats. Fine under a texture, wallpaper or a heavy coating. Joints will show under paint. |
| Level 4 | 0.60 | The normal domestic standard. Tape plus two or three coats, sanded. Correct under flat and matt paints. |
| Level 5 | 0.95 | Everything in level 4 plus a thin skim over the entire surface. Needed for gloss, satin, dark colours, and any wall hit by raking light from a window or a wall light. |
If you are not sure, look at where the light falls. A wall lit from the side at a shallow angle shows every joint at level 4; specify level 5 there and level 4 everywhere else.
Screws follow the spacing, not the sheet
The calculator uses 300 mm spacing along the sheet's end edges and 400 mm in the field — the spacing most building regulations expect for walls — and works out screws per sheet from your stud centres rather than quoting a flat number. A 1200 × 2400 sheet takes about 22 screws at 600 mm centres and about 30 at 400 mm centres, because the screw count follows the number of studs the sheet crosses. A 15% allowance is added for the ones you strip, overdrive or drop.
Tape is calculated from the joints, not the area
Board 1200 mm wide produces a vertical joint every 1200 mm, plus butt joints where sheets meet end to end, plus every internal corner. That works out at roughly 1.05 metres of tape for every square metre of board — useful because tape is sold in fixed roll lengths and running out mid-wall means a visible cold joint in the compound.
Board the ceiling first, then the walls. The wall sheets then hold the ceiling's edges up, the ceiling-to-wall joint closes tightly, and you are not trying to tape a gap that opens as the ceiling sags. This is also why the ceiling's perimeter joint is included in the tape figure.
Common questions
Should sheets run horizontally or vertically?
Horizontally on walls, in most cases. It puts the long tapered edges where they are easiest to finish, produces a single continuous joint at roughly waist height instead of several full-height joints, and the joint runs across the studs so it is stiffer. Vertical is used where the ceiling height matches the sheet exactly, or in commercial fire-rated details that specify it.
How much extra should I order?
The default 10% cutting waste is about right for a simple rectangular room. Push it to 15% if the room has several openings, a stairwell, or an awkward shape — and remember that an offcut from around a window is rarely big enough to use anywhere else.
Do I need moisture-resistant board?
In bathrooms and around sinks, yes — moisture-resistant board in the splash zones as a minimum. Behind a shower or a bath that will be tiled, neither standard nor moisture-resistant board is the right answer: use a cement backer board or a tile backer panel, which is what the tile adhesive and the waterproofing are designed to bond to.
Setting compound or ready-mixed?
Setting compound (the powder you mix, sold by working time) is harder, shrinks less and lets you do several coats in a day, so it is normally used for the tape coat and for filling gaps. Ready-mixed is softer and much easier to sand, so it is used for the finishing coats. Many jobs use both; the calculator gives you a total weight, which you then split between the two.
Why does the sheet count not simply divide area by sheet size?
Because a cut sheet rarely gets fully used elsewhere. The calculator divides by sheet area, applies the cutting waste and rounds up — which is the same thing a merchant's estimator does. For a small room with lots of openings the honest answer is that your real usage depends on how you plan the cuts, and planning them on paper first genuinely saves sheets.
Related
- Paint calculator — new board is porous and drinks the first coat
- Waste factor reference table
Method last reviewed 2026-09-18. Estimates for planning; local building regulations set the fixing centres and board specification.