Plasterboard sheet calculator

Pick a mode, punch in your measurements, and the sheet count updates as you type. Whole room takes the room's length, width and stud height, lets you toggle walls and ceiling, and deducts your doors and windows automatically. Single wall just takes an area in square metres, which suits a garage wall, a hallway or a patch job where you have already done the sums.

Then choose a sheet size. The count assumes you will use the offcuts sensibly, which is what the waste margin is for. Ten percent suits most rooms. Bump it up for rooms with lots of angles, wardrobes and bulkheads, and down toward five for one big plain wall.

The instinct is to pick the sheet size that wastes the least board. Resist it. Every joint you create has to be taped, stopped three times and sanded, and every joint is a place the eye can catch a flaw later. Board is cheap. Stopping is the expensive, skilled, slow part. So the pros pick the layout with the fewest joints, not the least offcut.

In practice that means the longest sheets you can carry and get into the room. Standard sheets here are 1200mm wide in lengths from 2.4m right up to 6m. On a 4m wall, one 3.6m sheet plus a 400mm piece beats two shorter sheets, because the single joint lands in one place instead of two.

On walls higher than 2.4m, look at the 1350mm wide sheets fixed horizontally. Two courses of 1350 covers a 2.7m stud exactly, with one horizontal joint at a comfortable working height instead of vertical joints every 1200.

Line the ceiling before the walls. The wall sheets then push up against the ceiling sheets and support their edges, which stiffens the whole junction and hides the ceiling sheet's cut edge inside the corner. Do it the other way round and you are fighting gravity while trying to leave a tidy edge on show.

Ceiling sheets are the heavy, awkward ones, so this is also the moment to be honest about help. Two people and a couple of T-props (or a hired panel lifter) make a ceiling a morning's work. One person and pride make it a chiropractor's invoice.

Bathrooms, laundries and toilets get wet-area board. GIB Aqualine is the one most merchants reach for, and Elephant AquaSmart is the equivalent. The core is treated to resist moisture, so an ordinary splash or a steamy mirror does not slowly turn the lining to porridge.

Two things people get wrong. First, wet-area board is not waterproofing. Behind a shower or over a bath, tiles need a proper waterproofing membrane applied over the board. The board is the substrate, the membrane is the raincoat. Second, standard board in a bathroom is not automatically illegal, but wet-area board is cheap insurance in the one room guaranteed to test it, so treat it as the default.

NZ finishing is graded under the joint Australia/NZ standard for gypsum linings (AS/NZS 2589), and the two levels you will actually hear quoted are Level 4 and Level 5. Level 4 is the default: joints, internal angles and screw heads taped and stopped with three coats, everything sanded flat, bare paper in between. Level 5 adds a thin skim coat of compound across the entire surface. You specify Level 5 where a wall gets raking light from a big window or wall wash lighting, or where the paint is semi-gloss, because those are the conditions that make Level 4 joints ghost through an otherwise perfect paint job. If a stopper quotes you "F4" or "F5" they mean the same two levels.

Hanging board is honest DIY territory: measure, cut with a knife and a snap, glue and screw. Screws go in until the head sits just below the surface without tearing the paper, roughly 200mm apart on sheet ends and 300mm elsewhere along the studs. Get a screw gun with a depth clutch and it is hard to get wrong.

Stopping is a different sport. Three coats, each wider than the last, feathered to nothing, then sanded under a raking light. A good stopper makes a wall disappear; a first-timer makes every joint a speed bump you will see for the next twenty years, because paint hides nothing. The honest play for most owner-builders: hang the board yourself, pay a professional stopper for the finish. You save the labour that is easy and buy the labour that is not.