Decking calculator

Enter the deck size, board width and gap — get the board count, linear feet, joists at your spacing, and screws. Works for wood and composite.

Units

Deck length (along boards)

Deck width (across boards)

Board size

Gap between boards

Joist spacing

Price per board (optional)

📐 You need

Estimates are for planning. Always confirm quantities with your supplier before ordering.

Frequently asked questions

How many deck boards do I need?

Rows = deck width ÷ (board width + gap), then divide the deck length by the board length for boards per row. A standard 1/4 in gap (5–6 mm) is included; the calculator adds 10% for cuts.

What joist spacing for decking?

16 in on center is standard for 5/4 wood decking perpendicular to joists. Composite boards and diagonal layouts usually require 12 in — check the board manufacturer's span chart.

How many screws per deck board?

Two screws at every board-joist intersection. A 12 ft board over joists at 16 in gets about 20 screws; the calculator counts intersections exactly.