Deck Calculator
Calculate how many deck boards you need, and compare piece counts across standard board lengths to minimize waste.
Extra material to cover cuts, mistakes, and offcuts.
Pieces needed by board length
A length that divides evenly into your deck's run wastes less material and leaves fewer joints.
How this is calculated
Boards across = deck width ÷ (board width + gap), rounded up. Linear length needed = boards across × deck length, then increased by your extra allowance.
Covers decking boards only — joists and footings aren't included yet.
How to measure a deck for decking boards
Measure the overall length and width of the deck, and the width of the boards you plan to use (check the product label — actual widths are often slightly less than the nominal size). Add the gap you'll leave between boards for drainage and movement.
The pieces-needed table compares a few standard board lengths so you can pick whichever wastes the least material for your deck's dimensions.
Frequently asked questions
How many deck boards do I need?
Divide the deck width by your board width plus the gap between boards to get the number of rows across, then multiply by the deck length to get total linear length. This calculator does that, then shows how many pieces you'd need at a few standard board lengths.
What gap should I leave between deck boards?
1/8 to 1/4 inch (about 3-6 mm) is typical for wood decking to allow for drainage and seasonal movement. Composite decking often has manufacturer-specific spacing — check your product's installation guide.
Which board length should I buy?
Compare the pieces-needed column for each length — a length that divides evenly into your deck's run wastes less material and leaves fewer end-to-end joints. Factor in price per board too, since longer boards often cost more per linear foot.
Does this include joists and footings?
Not yet — this calculator covers decking boards only. Joist and footing calculations are planned as a future addition.