Deck Board Calculator
Enter your deck size to get the boards you need, plus an estimated cost.
Boards needed
Estimated cost
How to calculate deck boards
Deck boards run side by side across the deck width. Convert the deck width to inches, then divide by one board's width plus the gap. Round up, because you cannot buy part of a board.
Formula: boards = deck width (in) ÷ (board width + gap), rounded up
Worked example: 16 ft × 12 ft deck, 6 in boards, quarter-inch gap
Deck width = 12 ft = 144 in. One board plus gap = 6.25 in. Boards: 144 ÷ 6.25 = 23.04, rounded up to 24 boards.
Board direction
This calculator assumes boards span the full deck length. If your boards are shorter than the deck, you need joints, and you should buy about 10% extra for offcuts.
Gap size
A quarter-inch gap is standard for wood boards, so water drains and boards can expand. Composite boards follow the maker's gap guide, which can be different.
Common deck sizes
Cost tips
Prices on this page are editable estimates, not quotes. Get 2 to 3 local quotes before you buy, and ask if delivery is included. Delivery, tax and waste can change the total a lot. Order a little extra for cuts and breakage, and confirm final quantities with your supplier or a qualified professional.
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Frequently asked questions
How many deck boards do I need for a 16x12 deck?
A 16 ft by 12 ft deck with 6 inch boards and a quarter-inch gap needs 24 boards, if the boards span the full 16 ft length.
What gap should I leave between deck boards?
About a quarter inch for wood boards, so water drains and boards can expand. Composite boards follow the maker's gap guide.
Which way should deck boards run?
Boards usually run along the long side of the deck. This calculator assumes boards span the full deck length.
What if my boards are shorter than the deck?
Then you need joints, and offcuts add waste. Buy 10% extra boards in that case.
Does this include joists and screws?
No, this counts deck boards only. Joists, screws, posts and rails are extra.
Are the prices accurate?
Prices are editable estimates. The defaults are typical US figures, and your local price can be higher or lower.