Cladding & Siding Calculator — Boards, Coverage & Fixings
Calculate linear metres or feet and board count for timber, fibre cement or composite cladding and siding. Enter wall dimensions, board width and overlap, and get total coverage including waste and fixing counts.
How much cladding or siding do I need?
Work from the covered area, not the boards' overall size. Subtract windows and doors from the wall area, divide by the board's visible cover width — the part still showing once the overlap is taken up — and add 10–15% for cuts, corners and gable ends.
What is cover width, and why does it matter?
An overlapping board hides part of itself. A 145 mm feather-edge or shiplap board may show only 120 mm once lapped; a nominal 6 in board often covers about 5 in. Size the job off the overall width and you finish roughly a fifth short. The declared cover width is on the product data sheet — that is the number to divide by.
Preview
Save to project
Free to try — no sign-up
Plan the whole job — not just this calculation
Save results to a project: budget and shopping list build themselves, and the whole plan exports as a PDF. Draw your floor plan and room sizes pre-fill the calculators.
How the cladding calculator works
- 1Calculate total wall area (m²), subtract windows and doors
- 2Effective module width = board width + open gap for decking/open-gap boards; for overlap cladding, enter the product's declared visible cover width as the board width and set the gap to 0
- 3Linear metres or feet = total area ÷ effective module width, rounded up with waste; the physical board count then depends on stock length and board orientation
- 4Linear metres or feet: board count × board length
- 5Fixings: 1–2 fixings per board per stud depending on board width and specification
- 6Apply 10–15% waste for cuts, corners and waste at 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. Approximately 330 fixings (1 fixing per stud, 15 stud lines × 22 courses at 600 mm / 24 in spacing).
Frequently asked questions
What is the standard overlap for cladding boards?
Feather-edge and shiplap boards typically have 25–40 mm (1–1½ in) overlap. Rebated boards interlock without exposed overlap. Always follow the manufacturer's installation instructions for the minimum headlap.
How much cladding do I need per m² of wall?
For 150 mm boards with 25 mm overlap (125 mm effective cover): 8 boards per metre of height = 8 linear metres 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 accounts for your specific board and overlap.
What wood is best for exterior cladding?
Larch, Siberian pine, western red cedar and oak are popular for durability. Pre-treated softwood (use a treatment class rated for the exposure under your local standard) is the most economical option. Thermally modified wood offers excellent stability without chemicals.
Do I need a ventilated gap behind cladding?
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. This prevents moisture build-up and extends the life of both the cladding and the wall.
How long does timber cladding last?
Properly maintained softwood cladding lasts 20–30 years. Hardwood and thermally modified wood 40–60 years. The key is regular maintenance — oiling or painting every 3–5 years depending on exposure.
Related calculators
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.