Siding Calculator
Project inputs
Use known net wall area when you already have a takeoff. Use perimeter mode for a quick rectangular building estimate.
Average wall height is used for corner trim and lap course estimates.
Corner trim
Results
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Formulas and assumptions
This estimator uses geometric coverage math. A siding square is 100 square feet of installed siding coverage. Product packaging, lap overlap, nailing requirements, starter strips, trim details, and installer layout rules can change the final order.
- Rectangular wall area:
perimeter x average wall height - Gable area:
gable count x gable width x gable rise / 2 - Net wall area:
gross wall area - openings - Waste-adjusted siding:
net wall area x (1 + siding waste% / 100) - Lap board coverage:
board length x exposed face height / 12 - Panel coverage:
panel width x panel height - Field pieces:
ceil(waste-adjusted siding / piece coverage) + additional pieces - Corner pieces:
corner height / trim length, rounded by the selected corner rounding method and trim waste allowance
How to measure siding
- Measure each wall face or measure the building perimeter and average siding height.
- Add triangular gable areas where siding continues above the eave line.
- Subtract large openings such as doors, windows, garage doors, and service panels when you want a tighter estimate.
- Enter the product's net coverage. For lap siding, use exposed face height after overlap, not the full board width.
- Count outside and inside corners separately, then set trim stick length and waste for cuts and splices.
Ordering limits
Use this as a planning and shopping-list estimate. It does not verify wall condition, flashing, weather barrier, fastener type, fire rating, wind zone, clearances, or local code. Confirm final quantities with the siding manufacturer, supplier, or installer before ordering.
Accessories such as starter strip, J-channel, window trim, soffit, fascia, house wrap, flashing tape, nails, caulk, and touch-up paint are outside this calculator.
Siding FAQs
Should openings be subtracted?
Subtract large openings for a tighter count. Many crews leave small windows or small service openings in the area to preserve a cutting buffer.
What waste percentage should I use?
Use about 10% for simple rectangular walls, 12% to 15% for normal remodeling, and 15% to 20% or more for many openings, short runs, steep gables, diagonal cuts, or fragile material.
Why do lap boards use exposed height?
Lap siding overlaps the row below. The exposed face height is the vertical coverage that remains visible and determines how much wall area each board covers.
How are corner pieces rounded?
Round each corner up when every corner needs full-height sticks or splices. Round total length only when offcuts can be combined across corners and the installer accepts that layout.