About & methodology

Deck Calculator is a free tool that estimates the materials and installed cost of a rectangular deck from its size and material. No sign-up; the math runs in your browser.

How the takeoff works

• Deck area = length × width.
• Deck boards = area ÷ one board's coverage (5½″ × board length), + 10% waste.
• Joists = (length × 12 ÷ joist spacing) + 1; total length = joists × width.
• Footings ≈ two beam lines with posts ~8 ft on center.
• Deck screws ≈ 2.5 per square foot.
• Installed cost = area × a per-square-foot range for the material.

Important

These are planning estimates for a simple rectangular deck. Beams, ledger boards, railings, stairs, and footing depth depend on deck height, span tables, and local code. Confirm with a contractor and your building department before you build.