Results update as you type. Round up when ordering.
Based on 5/4×6 deck boards (5.5 in actual width) with 1/8 in gaps. Check your board's actual width.
Formula checked against manufacturer specs
Rounded up to whole units
Runs in your browser
How deck boards are counted
Divide the deck width (perpendicular to the boards) by the board's face width plus the gap to get the number of rows. Multiply rows by deck length for linear feet, add waste, and divide by your board length.
Example: 16 × 12 ft deck, 5.5 in boards with 1/8 in gaps: 144 ÷ 5.625 = 25.6 → 26 rows × 16 ft = 416 linear ft. Plus 10% = 457.6 ÷ 16 = 28.6 → 29 boards.
Gaps and materials
Pressure-treated pine is often installed tight because it shrinks as it dries; follow the lumber supplier's advice.
Composite decking: use the manufacturer's spacing (commonly around 3/16 in) and hidden fasteners where specified.
Fasteners
Face-screwing uses two screws at every joist. With joists 16 in on center, that's about 350 screws per 100 sq ft—buy coated or stainless screws rated for treated lumber.
It uses the standard formula shown on this page and rounds bags, boxes and pieces up to whole units. Product sizes vary by brand, so confirm with the label or your supplier before you buy.
Should I buy extra material?
Yes. A 5–10% allowance covers cuts, spills and uneven surfaces; running short mid-job usually costs more than a few leftovers.
Is this calculator free?
Yes. Every PorchMath calculator is free, needs no account and runs entirely in your browser.