Decking Calculator

ft
ft
in
5/4×6 decking face width: 5.5 in. Composite 1×6: 5.4 in.
in
Construction

Calculate the number of deck boards needed based on deck dimensions and board width.

Formula

Boards = deck width (in) / (board width + gap); +5% waste
  • Gap: allow 1/4 in for composite; 1/8 in green lumber (expands when dried).
  • Add 5–10% for waste and cuts.

20×12 ft deck, 5.5 in boards, 1/4 in gap

Inputs
  • Deck Length: 20 ft
  • Deck Width: 12 ft
  • Board Width (face): 5.5 in
  • Gap Between Boards: 0.25 in

144 in / 5.75 = 25 boards × 20 ft = 500 lf + 5% = 525 lf.

Frequently asked questions

How long do deck boards typically come?
Standard lengths: 8, 10, 12, 16, and 20 feet. Choose lengths that minimize waste.