Siding Calculator — Boards, Coverage & Fasteners
Calculate how much siding you need for exterior walls: board count, total coverage and fasteners for lap siding, shiplap and board profiles in timber, fibre cement or composite. Enter wall dimensions and your board's exposure width.
How the siding estimate works
- 1Calculate total wall area, subtract windows and doors
- 2Effective cover = the board's exposed (visible) width after overlap — use the manufacturer's declared cover width
- 3Courses = wall height ÷ effective cover; running length = courses × wall width
- 4Board count: running length ÷ stock board length, rounded up
- 5Fasteners: 1–2 per board per stud line depending on board width and specification
- 6Apply 10–15% waste for cuts, corners and gable ends
Worked example
Wall: 8 m wide, 2.7 m high. Boards 150 mm wide with 25 mm overlap — effective cover 125 mm.
You need 22 board courses. At 8 m per course: 176 linear metres of board. With 10% waste: 194 lm, and approximately 330 fasteners at 600 mm stud spacing.
Frequently asked questions
How much siding do I need per m² of wall?
For 150 mm boards with 25 mm overlap (125 mm effective cover): 8 linear metres of board per m² of wall. The calculator adjusts for your exact board and overlap.
What is the standard overlap for lap siding?
Feather-edge and lap profiles typically overlap 25–40 mm; rebated/shiplap boards interlock without exposed overlap. Follow the manufacturer's minimum headlap.
Do I need a ventilation gap behind siding?
Yes — a ventilated air gap behind the cladding (commonly around 20–25 mm) is widely recommended and required by many building standards. It prevents moisture build-up and extends the life of the wall.
How long does timber siding last?
Properly maintained softwood siding lasts 20–30 years; hardwood and thermally modified wood 40–60 years. Regular refinishing every 3–5 years is the key variable.