How many board and batten do I need?

A 3.6 m by 2.4 m wall with 150 mm boards and 20 mm gaps takes 21 boards and 20 battens — with 10% extra for mistakes, buy 24 boards and 22 battens. On a 2.4 m wall every piece is a full 2.4 m length with nothing cut off, which is why this wall is the cheapest kind to build.

Whatever your batten can cover. The gap is the shadow line between boards and the batten sits right over it, so a 25×50 mm batten comfortably covers gaps from 15 mm to 25 mm. Whatever width is left over after fitting whole boards gets spread evenly across every gap — that keeps the rhythm looking even instead of one fat gap at the end of the wall.

Square-edge PSE (planed, square edge) boards from 100 mm to 200 mm wide, with 25×38 mm or 25×50 mm battens. The calculator uses the widths you can actually measure — check one board with a tape before you commit to the whole wall, because planed sizes vary a millimetre or two between merchants.

Only if the end is exposed. Where the wall runs into a corner, the corner itself is the trim and a batten there would just look cluttered. Chimney breasts, hallway stub walls and half walls usually want the two end battens — there is a checkbox for it in the advanced options.

Then buy longer stock. A 2.7 m wall built from 2.4 m lengths means every board needs a scarf joint — twice the pieces and twice the seams to fill. Victorian ceilings in particular run tall; the stock length dropdown is where you fix it, and 3.0 m and 3.6 m lengths are standard at most merchants.

A 3.6 m by 2.4 m wall with 150 mm boards runs about £330 all-in at typical merchant prices: 24 boards at £11, 22 battens at £4.50, plus a box of brads and a tube of adhesive. Paint is extra. Type your own prices into the cost panel and the total follows.