Deck board calculator
How many deck boards to buy?
Enter the size of your deck, pick a board and a gap, and see the number of boards, the linear feet and a top-down drawing of the layout before you order.
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How the count is built
Boards run along the length of the deck. The calculator works out how many rows fit across the width once each board and its gap is counted, then how many pieces each row needs, rounding up at each step. The total adds your waste allowance and rounds up to whole boards.
- Board width is the actual width after milling. A 2 × 6 or 5/4 × 6 board is usually about 5½ inches wide, not 6.
- Gap is the space between boards for drainage and expansion. Many builders use about an eighth of an inch, but check the decking maker’s spacing.
- Waste covers offcuts, damaged boards and the stairs or borders. Ten percent is a common starting figure.
What to check before you order
Stagger the joints so each board end sits on a joist, and mark where the boards will cross them. Check local rules for railings and footings, and confirm the board length you choose is sold at your yard. This page gives an estimate, not a structural plan.
Estimates that become invoices
Quote from real job data
ScopeBid: Estimate & Invoice is a free iPhone and iPad app by James Gray for independent tradespeople such as painters, cleaners and landscapers. It reuses pricing from past jobs so new quotes start from real numbers.
Build quotes from saved jobs, templates or scratch, with Profit Guard showing margin and markup. Make PDF quotes and invoices, take on-screen signatures, and track deposits. It works offline, with no account required.
Get ScopeBid on the App StoreFree to download, with in-app purchases. The first three quotes include full PDFs. ScopeBid Pro unlocks unlimited quoting and the full invoicing and costing tools. Requires iOS 18 or later. Details checked against the App Store listing on November 10, 2026.
Publisher disclosure: Honest Little Apps publishes both ScopeBid and this page. This is not an independent review. This page is a separate web companion, not a feature of the app. This deck board calculator is a free web tool from the same publisher. It is an estimate for planning and does not replace a site survey or structural design.
Deck board questions
How many deck boards do I need for a 12 by 16 foot deck?
With 5½-inch boards, a 1/8-inch gap and 12-foot boards, a 16 by 12 foot deck needs 26 rows of two pieces, which is 52 boards before waste. A ten percent allowance brings the total to 58.
Should boards run lengthwise or across the deck?
Usually lengthwise, which uses fewer joints. The calculator assumes boards run along the length, so check the layout for your deck before you order.
Why do I need a waste allowance?
Some boards are cut short, damaged or used for stairs and borders, so a small extra amount prevents running short partway through the job.
Is the estimate a substitute for a survey?
No. It gives board counts for planning. For railings, footings, ledgers and loads, check local code and speak with a qualified builder.
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