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Deck Material Calculator
Estimate deck boards, joists, screws and cost from the deck size, board width, board length and joist spacing, with a waste allowance.
How to use it
- Enter the deck length (the direction the boards run) and width (the direction the joists span).
- Pick the board width and the length you will buy; matching board length to deck length avoids seams and waste.
- Use 16 inch joist spacing for typical decking, or 12 inch for diagonal patterns and composite.
- Add waste for cuts, defects and picture-frame borders.
How it works
Rows of boards = deck width ÷ (board width + gap). Each row needs ceil(length ÷ stock length) pieces, and boards cut from the same stock length are best planned in a staggered layout. Joists run across the width: count = length ÷ spacing + 1. Screws are estimated at two per board-joist crossing plus 5 percent.
Check your local building code for joist span tables, footing sizes and ledger attachment; this calculator covers surface material and joist count only, not beams, posts or hardware.
FAQ
How many deck boards do I need for a 12x12 deck?
With 5.5 inch boards and a 1/8 inch gap, a 12x12 deck needs about 26 rows; using 12 ft boards that is 26 boards plus about 10 percent waste, so 29.
How many screws per square foot of decking?
About 2.5 to 3 screws per square foot with 16 inch joist spacing and 5.5 inch boards (two per crossing).
What joist spacing should I use for composite decking?
Most composite manufacturers require 12-16 inch spacing (12 inch for diagonal or high-traffic areas). Always follow the product instructions.
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