Cladding boards calculator
How many boards a wall takes once the overlap is accounted for.
Fill in the fields and the result will appear here automatically.
Works out how many boards a wall needs when they are laid with an overlap. The overlap is the whole point of the correction: a 190 mm board lapped by 20 mm only covers 170, so dividing wall area by board area undercounts by roughly a tenth. This differs from costing boards by the cubic metre — that answers volume and price, this answers coverage, and the result is measured in pieces and linear metres.
How it works
Formula and logic
Effective width beff=b−o. Purchase area Aw=A·(1+w/100); boards n=⌈Aw/(L·beff)⌉; linear metres=n·L. Width lost to overlap is o/b·100%. A, L and b are positive and finite, 0≤o<b, and allowance w is 0–50%. This area estimate does not lay out rows or reuse offcuts.
Example
A 30 m² wall with 3 × 0.19 m boards, a 0.02 m overlap and 10% waste takes 65 boards — 195 linear metres.
Fields and units
- Wall area — m²
- Board length — m
- Board width — m
- Overlap — m
- Cutting waste — %
How to use
- — Enter the wall area, leaving openings in if you want them as extra allowance.
- — Give the catalogue length and full width of the board.
- — Set the overlap — how far neighbouring boards cover each other.
- — Choose an allowance from your layout, from 0 to 50%.
Method and limitations
- Calculation method
- Formula and logic
- Limitation
- This area estimate does not lay out rows or reuse offcuts.
FAQ
Why not just divide the area by the board area?
Because the overlap eats part of every board. At 190 mm wide with a 20 mm lap only 170 mm works, and without that correction you fall short by roughly a tenth.
How is this different from costing boards by volume?
That answers cubic metres and price. This answers coverage with the overlap included, and the result is pieces and linear metres.
What overlap should I use?
Use the actual profile dimensions and installation layout. Enter the difference between full and covering width; there is no universal overlap for every joint.
Should I subtract windows and doors?
You can, but then raise the allowance: short offcuts above and below openings rarely all get used.