Enter the size of the deck and the boards you plan to use. The calculator works out how many rows of boards cover the deck, how many boards to buy in the length you pick and how many face screws you need.
How the deck board calculator works
- Rows = deck width ÷ (board width + gap), rounded up. Boards run along the deck length.
- Boards: if one board is at least as long as the deck, each board covers one row (or two, if it is twice as long). Short offcuts are not counted as reusable. On longer decks, boards are joined over joists and the calculator uses the total length.
- Extra of 10% covers end trims and boards with defects.
- Screws = rows × joists × 2, with two screws per board at every joist.
Most decking sold as 5/4×6 or 2×6, and most composite boards, are 5.5 in wide. The gap and fasteners differ by product, so check the maker’s instructions.
Worked example
A 16 × 12 ft deck with 5.5 in boards and a 3/16 in gap needs 144 ÷ 5.6875 = 25.3, so 26 rows. With 16 ft boards each row takes one board; adding 10% gives 28.6, so 29 boards. Joists at 16 in spacing give 13 joists, so you need 26 × 13 × 2 = 676 screws.
Boards for common deck sizes
5.5 in boards, 3/16 in gap, 10% extra. Deck size is length (along the boards) × width.
| Deck (ft) | Rows | 12 ft boards | 16 ft boards | 20 ft boards |
|---|---|---|---|---|
| 10 × 10 | 22 | 25 | 25 | 13 |
| 12 × 12 | 26 | 29 | 29 | 29 |
| 16 × 12 | 26 | 39 | 29 | 29 |
| 16 × 16 | 34 | 50 | 38 | 38 |
| 20 × 16 | 34 | 63 | 47 | 38 |
| 20 × 20 | 43 | 79 | 60 | 48 |
Matching the board length to the deck length saves the most material: a 10 ft deck uses 20 ft boards cut in half with almost no waste.
Step by step: buying deck boards
Tips before you order
- Use the screws or hidden fasteners your board maker specifies; the wrong ones can void the warranty. Screws are usually sold in 5 lb boxes of about 330 to 380 #10 × 3 in screws, so the calculator also gives the number of boxes.
- When the deck is built, the deck stain calculator estimates the stain, and the concrete footing calculator covers the footings.
- Stagger butt joints on long decks and land every joint on a joist, often with an extra block.
- Joist spacing for composite boards is often 16 in, and 12 in for diagonal layouts. Check the product limits.
- Pressure-treated boards shrink as they dry, so they are often laid tight and the gap opens later.
