Deck Calculator
Enter your deck length and width, board size, gaps and joist spacing to estimate the boards and joists to buy.
Your details
Result
Decking boards
29
26 rows + 10% waste
- Joists
- 13
- Board linear feet
- 464 ft
- Joist linear feet
- 156 ft
- Deck area
- 192 ft²
- Boards run along the deck length; joists span the width. Verify span tables and local codes for your lumber size.
Good to know: A 16 ft × 12 ft deck needs about 28 boards and 13 joists with a 10% waste allowance.
Please note: Estimates only. Measure your actual space, buy a little extra, and check product labels, safety requirements and local building rules. Do not rely on this for structural or safety-critical work.
Questions people ask
How are joists calculated?
One joist at each spacing interval across the length, plus one to close the end.
What gap should I leave between boards?
About 1/4 inch, or as recommended by the decking manufacturer.
Does this replace span tables?
No. Check joist size and span against local building codes.
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How we calculate this
We use the standard published formula or definition for this calculation, and we show the working so you can check it.
Spotted a mistake? Tell us and we'll check it. How we check our calculators