The formula
boards = area × sides × (1 + allowance) ÷ (board width × height)
Where it comes from
Counting boards is easy: the area divided by the three square metres of a standard 1.20 × 2.50 board, times the number of sides. What throws quotations out is everything else. A partition takes vertical studs every 60 cm — every 40 if anything heavy is going on it — track top and bottom, around twenty-five screws per board, and tape with three coats of compound on every joint. None of that comes out of the board count and all of it turns up on the invoice.
How to work it out by hand
- Multiply the area by the number of sides
- Add the cutting allowance
- Divide by the area of one board
- Space the studs every 60 cm along the partition, and add one
What is worth knowing
Insulation goes in once, inside the partition, even though the boards are on two sides: that is the most repeated mistake when ordering. Stud spacing is not cosmetic: at 60 cm the wall holds a picture, at 40 cm it holds a television, and for a kitchen unit or a radiator you need timber or steel noggins between studs, decided before the wall is closed. Joints want three coats of compound with sanding between them: the first beds the tape, the second covers it and the third feathers it out. Skipping the third shows in raking light for ever.