The board count is the easy part. The number that decides how long the job takes and how it looks is the number of joints — and that is set by which board length you buy, which almost no calculator asks about.
Walls and ceilings. Enter the area and the board size, and get whole boards.
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The board count is straightforward arithmetic. What decides how long the job takes and how the wall looks is how many joints there are — and that is set by which board length you buy, which almost no calculator mentions. Choose the longest board that fits the room and gets through the door. A horizontal joint in the middle of a wall is work you have chosen to create, and it is the hardest kind to hide.
A joint running out of a door or window corner will crack, every time, because that is exactly where movement concentrates. Plan the boarding so joints break bond like brickwork and no joint lines up with the corner of an opening. This is layout thinking rather than quantity thinking, and it costs nothing if done before the delivery arrives.
Board the ceiling first, then the walls, so the wall boards support the ceiling edges. The other way round leaves the ceiling perimeter unsupported, which is the usual cause of a cracked ceiling line. And a board is heavier than it looks: a 2.4 m sheet of 12.5 mm board is around 20 kg and a 3 m sheet closer to 25 — boarding a ceiling alone is not realistic without a board lifter. Screw at 150 mm along edges and 230 mm in the field, and the screw should dimple the paper without breaking it, because a screw through the paper holds nothing.
The longest that fits the room and gets through the door. Board length changes the number of joints far more than it changes the number of boards, and joints are what take the time and show in the finish.
Ceiling first, then walls. The wall boards then support the ceiling edges. Doing it the other way round leaves the ceiling perimeter unsupported, which is the usual cause of a cracked ceiling line.
Because movement concentrates there. A board joint running out of an opening corner will crack every time, so plan the layout so no joint lines up with the corner of a door or window.
Around 150 mm along the edges and 230 mm in the field. The screw should dimple the paper without breaking through it — a screw driven through the paper holds nothing at all.