Lap Siding Calculator

Lap siding — horizontal boards that overlap course over course — is the most common exterior in North America, and it all follows one estimating rule regardless of material. Coverage per board depends on the reveal (the exposed height of each course); your board count is net wall area, plus waste, divided by that coverage. Pick your material and the tool sets sensible defaults you can override.

Because every lap product converts to squares, this page is a quick way to compare vinyl lap, Hardie lap, LP and wood on the same footing before you commit.

The same 2,000 sq ft of wall covered at a wider reveal needs fewer boards than at a tighter reveal — but it's still 20 squares. Squares measure the wall; boards measure how you cover it.

We'd rather be transparent than falsely precise. The quantity math is deterministic and matches standard takeoff practice, so if your inputs are right, your squares and piece counts are right. Where real-world variation lives — coverage by profile, and installed cost by region and crew — we use typical published figures and present them as ranges. That makes this a strong planning number, not a binding quote; a contractor's field measure remains the final word.

One figure rarely tells the whole story. Confirm these points and your lap siding estimate becomes an order you can actually place with confidence.

• Confirm coverage: the default coverage is a planning figure. Check the exact coverage printed on your product's box or spec sheet and adjust it if it differs, since even a small change moves the piece count on a big wall.
• Match the waste to your walls: keep 10% for a simple rectangular house, and raise it toward 15% for gables, dormers, bay windows and lots of angled cuts, because those details generate short offcuts you can't reuse.
• Account for accessories: starter strip, trim, inside and outside corners, flashing and fasteners are all part of a complete order, not an afterthought — the takeoff above estimates each so your material list is whole.
• Keep a spare: hold back a piece or a full box for future repairs, since profiles and colors get discontinued over time and an exact match years later is hard to find.
• Time your order: have material delivered close to the start date, stored flat and dry, so it isn't sitting exposed or getting damaged before the crew arrives.

Re-run the numbers above after any change and lean on the per-wall audit to verify each surface one at a time, so what you order matches what the wall actually needs rather than a rough guess. That small habit is the difference between one clean delivery and a mid-project trip back to the supplier.