Deck Board Calculator
Enter your deck dimensions and board size to get the number of decking boards to buy.
Enter your measurements to see what to buy.
How to calculate it
Enter your deck dimensions and board size to get the number of decking boards to buy.
Source: Rows = deck width ÷ (board width + gap); boards per row = deck length ÷ board length; total × waste. A 5/4×6 board has an actual width of 5.5 in.
A 12×16 ft deck, 5.5 in boards, 1/8 in gap, 12 ft boards, 10% waste: rows = (12×12) ÷ 5.625 = 26; per row = 16÷12 = 2; boards = 26×2×1.1 = 58 boards.
Purchasing & waste guidance
- A standard 5/4×6 board has an actual width of 5.5 in.
- Composite boards are often 5.25–5.5 in wide — check the spec sheet.
- Leave a 1/8 in gap for composite, up to 1/4 in for wet pressure-treated wood (it shrinks).
- Longer boards mean fewer butt joints — use 16 or 20 ft boards when the deck allows.
- Plan about 350 screws per 100 ft² of decking for face-fastened boards.
Assumptions & what’s included
- Boards run along the deck’s length; rows span the width.
- Board width and gap are in inches; board length is the stocked length in feet.
- Waste allowance covers cuts and defects. Price is per board and optional.
Frequently asked questions
How many deck boards do I need for a 12×12 deck?
A 12×12 ft deck with 5.5 in boards, 1/8 in gaps and 12 ft boards needs about 27 boards with a 10% waste allowance. The calculator adjusts for any board length.
What gap should I leave between deck boards?
About 1/8 in for composite decking and up to 1/4 in for wet pressure-treated wood, which shrinks as it dries. Dry wood needs a smaller gap.
How many screws do I need for a deck?
Plan on roughly 350 screws per 100 ft² of decking for face-fastened boards. Hidden-fastener systems list their own coverage per box.