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.
Exterior wall build-up
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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 — 26 × 9 ft. Boards 150 mm wide with 25 mm overlap, so effective cover is 125 mm: a nominal 6 in board showing 5 in.
You need 22 board courses. At 8 m per course: 176 linear metres of board. With 10% waste: 194 lm — about 636 linear feet — and approximately 330 fasteners at 600 mm (24 in OC) 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 — in US sizes, a 6 in board showing 5 in gives about 2.4 linear feet per square foot. 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 (1–1½ in); 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, or ¾–1 in) 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.
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Tools for this job
This is the same kit as decking. The deck building tools guide — what each one does, what to skip, and what it costs to buy or rent.