Deck Board Calculator

How deck board quantities are calculated

Each board covers its own width plus one gap, and the boards run the length of the deck, so:

Boards = deck width in inches ÷ (board width + gap), rounded up
Linear feet = boards × deck length

Use the ACTUAL board width. Both a 2×6 and a 5/4×6 deck board measure 5.5 inches wide in reality (the "6" is the nominal name), and most composite decking is 5.5 inches too. Enter 5.5 for any standard "6-inch" board, or measure yours if it's a specialty profile. The gap matters: pressure-treated lumber is usually installed with about a 1/4-inch gap that shrinks as the wood dries, while composite manufacturers typically specify 3/16–1/4 inch for drainage and expansion — check your board maker's spec.

The screw estimate assumes two screws at every joist each board crosses: crossings = deck length ÷ joist spacing, plus the end joist. Hidden-fastener clips follow the same one-per-crossing logic (one clip per board per joist). Add roughly 10% for dropped and defective fasteners.

Buying lengths: if the deck length falls between standard board lengths (8, 10, 12, 16, 20 ft), buy the next length up and count the cutoffs in your waste allowance, or plan a seam pattern with butt joints staggered over joists. Diagonal layouts look great but push waste toward 15% and require 12-inch joist spacing in many cases.