★ CONSTRUCTION · DECKING · SCREW SPACING
A 16 ft by 12 ft deck at 16-in joist spacing with 5.5-in boards needs 700 screws — 35 boards at 20 screws each, 364.58 per 100 sq ft. Screws per board by joist spacing (12, 16, 24 in) and board width (5.5, 7.25 in), screws per 100 sq ft, plus a calculator for any deck. This one is the SPACING table — screws per board and per 100 sq ft by spacing and board width — the deck-screw-chart page is the SIZE/LENGTH + COUNT page — screw sizes and lengths and the count for one deck (1,120 screws for a 20 by 16 ft deck) — not the spacing table; and the drywall-screw-spacing-chart page is the same template for a different material — drywall sheets, not deck boards.
Put your deck length, width, joist spacing and board width in: 16 ft by 12 ft at 16-in spacing with 5.5-in boards is 700 screws, 20 per board. The table gives all five numbers for every spacing and board width.
700 screws — 35 boards at 20 screws each, 364.58 per 100 sq ft. A 12-ft board length at 16-in joist spacing crosses 10 joists (144 ÷ 16, plus one for the end joist), and 2 screws at every crossing is 20 screws per board. A 16-ft run of 5.5-in boards with a 1/8-in gap needs 35 boards (192 ÷ 5.625, rounded up). Thirty-five boards times 20 screws is 700, and 700 screws over 192 sq ft is 364.58 per 100 sq ft. That is the whole calculation: joists from the width and spacing, boards from the length and board width, screws per board from the joists, and the total from the boards. The table above gives all five numbers for every combination of 12, 16 and 24-in spacing with 5.5 and 7.25-in boards, so the same arithmetic works for any deck.
| Joist spacing & board width | Joists | Boards | Screws per board | Total screws | Screws per 100 sq ft |
|---|---|---|---|---|---|
| 12-in spacing, 5.5-in boards | 13 | 35 | 26 | 910 | 473.96 |
| 12-in spacing, 7.25-in boards | 13 | 27 | 26 | 702 | 365.63 |
| 16-in spacing, 5.5-in boards | 10 | 35 | 20 | 700 | 364.58 |
| 16-in spacing, 7.25-in boards | 10 | 27 | 20 | 540 | 281.25 |
| 24-in spacing, 5.5-in boards | 7 | 35 | 14 | 490 | 255.21 |
| 24-in spacing, 7.25-in boards | 7 | 27 | 14 | 378 | 196.88 |
Two screws at every board-joist crossing is the industry standard — engineerfix.com ("industry standard of using two screws at every point where a deck board crosses a joist"), trexprotect.com ("two screws per joist") and chippy.tools ("two screws per board per joist crossing") all agree. Joist count is the span divided by the spacing, plus one, rounded up — chippy.tools ("(deck width / joist spacing) + 1, rounded up"); engineerfix's 16-ft board at 16-in spacing crosses 13 joists (192/16 + 1). Boards are counted with a 1/8-in gap — 5/4 decking is spaced 1/8 in to 3/8 in apart (plasticinehouse.com) — so a 16-ft run of 5.5-in boards needs 35 boards, not 34. Spacing guidance: 16 in on center suits most decking run perpendicular to the joists, 12 in for diagonal decking or composite boards, 24 in for 2x6 decking (plasticinehouse.com). The table is for a 16 ft by 12 ft deck (192 sq ft); the calculator above works out any deck size, spacing and board width. Order about 10% over the total for dropped screws and stripped heads (chippy.tools).
The joist count includes the end joist — that is where counts go wrong. A 12-ft span at 16-in spacing is not 9 joists (144 ÷ 16) but 10: joists at 0, 16, 32, 48, 64, 80, 96, 112 and 128 in, plus the rim joist at 144 in. Miss the end joist and every board is 2 screws short — 70 screws short on this deck. The formula is the span divided by the spacing, rounded up, plus one, and it is the same formula whether the span divides evenly or not: an 11-ft span at 16-in spacing is ceiling(132 ÷ 16) + 1 = 10 joists, the same 20 screws per board as the 12-ft span, which is why 11 ft is the narrowest width with 20 screws per board at this spacing and 10 ft drops to 18. Count the joists on the frame, not on the calculator, and the two should agree.
The gap changes the board count, and the board count changes everything. Boards are counted with a 1/8-in gap in this model, because 5/4 decking is spaced 1/8 in to 3/8 in apart and the gap eats length: 192 in ÷ 5.625 in is 34.13, rounded up to 35 boards, while ignoring the gap gives 192 ÷ 5.5 = 34.91, still 35 here — but on a longer run the gap flips the count, and every extra board is another 20 screws. A 1/4-in gap instead of 1/8 in takes this deck from 35 boards to 34 (192 ÷ 5.75 = 33.39, rounded up), and 20 fewer screws. The gap is a choice, not a constant: wood shrinks as it dries and can be laid tighter, composite expands with heat and needs its specified gap, so follow the board manufacturer's gap and the board count follows. The screws per board never change with the gap — only the number of boards does.
The spacing is a structural choice first and a screw count second. Sixteen inches suits most decking run perpendicular to the joists; diagonal decking and many composite boards need 12 in, which takes this deck from 700 screws to 910; 2x6 decking allows 24 in, which drops it to 490. Do not widen the spacing to save screws — the spacing is set by the board span rating and the layout, and a board that bounces or sags has cost more than the screws saved. The per-100-sq-ft column is the comparison that survives any deck size: 473.96 at 12-in spacing with 5.5-in boards, 364.58 at 16-in, 255.21 at 24-in, and 196.88 at 24-in with 7.25-in boards. The mined rule of thumb of about 350 screws per 100 sq ft sits next to this page's 364.58 for the standard 16-in, 5.5-in deck — the same order, and the table's exact count is the better number for ordering.
On the defaults: a 16 ft by 12 ft deck, 16-in joist spacing, 5.5-in boards, 1/8-in gap.
And the other way: the shortest deck length reaching 700 screws is 16 ft, the joists for 20 screws per board are 10, and the narrowest deck width with 20 screws per board at 16-in spacing is 11 ft.
The defaults are a 16 ft by 12 ft deck, 16-in joist spacing, 5.5-in boards and a 1/8-in gap. Boards run across the width, so the board length is the deck width and the joists are counted across it; the board count runs along the length. Two screws at every board-joist crossing is the industry standard, agreed by three independent sources, placed about 3/4 in to 1 in from the board edges and in a straight line, not staggered. The joist count is the span divided by the spacing, rounded up, plus one for the end joist. The board count is the length divided by the board width plus the gap, rounded up — a 1/8-in gap in this model, inside the published 1/8-in to 3/8-in range for 5/4 decking. The model counts face screws only: hidden fastener systems have their own coverage rating per square foot and are not counted here, and diagonal or herringbone layouts cross more joists per board than straight runs. It does not add waste — order about 10% over the total for dropped screws and stripped heads — and it does not count screws for stairs, railings, fascia or framing. The screw length and gauge are a separate choice: 2-1/2-in screws for 5/4 decking and 3-in to 3-1/2-in for 2x decking, per the site's own deck-screw-chart, and the board manufacturer's directions govern.
These notes repeat in every explainer section because this page is built to be read start to finish: the joist count includes the end joist; the gap changes the board count; and the spacing is a structural choice first and a screw count second.
| Output | Formula | What it means |
|---|---|---|
| Joists | ceiling(width in inches ÷ spacing) + 1 | 10 joists — ceiling(144 ÷ 16) + 1. |
| Boards | ceiling(length in inches ÷ (board width + 1/8-in gap)) | 35 boards — ceiling(192 ÷ 5.625). |
| Screws per board | joists × 2 | 20 screws per board — 10 × 2. |
| Total screws | boards × screws per board | 700 screws — 35 × 20. |
| Screws per 100 sq ft | total screws ÷ deck area × 100 | 364.58 per 100 sq ft — 700 ÷ 192 × 100. |
| Deck area | length × width | 192 sq ft — 16 × 12. |
| Reverse: Shortest deck length reaching 700 screws | step | 16 ft long: 16 ft × 12 ft deck, 16-in joists, 5.5-in boards: 10 joists, 35 boards, 20 screws per board — 700 screws, 364.58 per 100 sq ft. |
| Reverse: Joists for 20 screws per board | step | 10 joists: 10 joists give 20 screws per board (2 screws per joist). |
| Reverse: Narrowest deck width with 20 screws per board | step | 11 ft wide: 16 ft × 11 ft deck, 16-in joists, 5.5-in boards: 10 joists, 35 boards, 20 screws per board — 700 screws, 397.73 per 100 sq ft. |
| 20 ft long deck instead of 16 ft | same model | 20 ft × 12 ft deck, 16-in joists, 5.5-in boards: 10 joists, 43 boards, 20 screws per board — 860 screws, 358.33 per 100 sq ft. |
| 12 ft long deck instead of 16 ft | same model | 12 ft × 12 ft deck, 16-in joists, 5.5-in boards: 10 joists, 26 boards, 20 screws per board — 520 screws, 361.11 per 100 sq ft. |
| 16 ft wide deck instead of 12 ft | same model | 16 ft × 16 ft deck, 16-in joists, 5.5-in boards: 13 joists, 35 boards, 26 screws per board — 910 screws, 355.47 per 100 sq ft. |
| 12-in joist spacing instead of 16 in | same model | 16 ft × 12 ft deck, 12-in joists, 5.5-in boards: 13 joists, 35 boards, 26 screws per board — 910 screws, 473.96 per 100 sq ft. |
| 24-in joist spacing instead of 16 in | same model | 16 ft × 12 ft deck, 24-in joists, 5.5-in boards: 7 joists, 35 boards, 14 screws per board — 490 screws, 255.21 per 100 sq ft. |
| 7.25-in boards instead of 5.5 in | same model | 16 ft × 12 ft deck, 16-in joists, 7.25-in boards: 10 joists, 27 boards, 20 screws per board — 540 screws, 281.25 per 100 sq ft. |
| 10 ft wide deck instead of 12 ft | same model | 16 ft × 10 ft deck, 16-in joists, 5.5-in boards: 9 joists, 35 boards, 18 screws per board — 630 screws, 393.75 per 100 sq ft. |
| 12-in spacing with 7.25-in boards | same model | 16 ft × 12 ft deck, 12-in joists, 7.25-in boards: 13 joists, 27 boards, 26 screws per board — 702 screws, 365.63 per 100 sq ft. |
| 0 ft by 0 ft deck | same model | 0 ft × 0 ft deck, 16-in joists, 5.5-in boards: 1 joists, 0 boards, 2 screws per board — 0 screws, 0.00 per 100 sq ft. |
| 1 ft by 1 ft deck | same model | 1 ft × 1 ft deck, 16-in joists, 5.5-in boards: 2 joists, 3 boards, 4 screws per board — 12 screws, 1,200.00 per 100 sq ft. |
| 40 ft by 20 ft deck | same model | 40 ft × 20 ft deck, 16-in joists, 5.5-in boards: 16 joists, 86 boards, 32 screws per board — 2,752 screws, 344.00 per 100 sq ft. |
| 24-in spacing on the headline deck | same model | 16 ft × 12 ft deck, 24-in joists, 5.5-in boards: 7 joists, 35 boards, 14 screws per board — 490 screws, 255.21 per 100 sq ft. |
Figures are the model's own counts on the numbers you type, computed from unrounded values: the joists are the width in inches divided by the spacing, rounded up, plus one; the boards are the length in inches divided by the board width plus a 1/8-in gap, rounded up; the screws per board are the joists times 2; the total is the boards times the screws per board; and the screws per 100 sq ft are the total divided by the deck area times 100. The displayed figures are rounded to 2dp where they are not whole. The 2-screws-per-crossing standard is agreed by three independent sources; the joist formula is the published span-divided-by-spacing-plus-one rule, rounded up; the 1/8-in gap sits inside the published 1/8-in to 3/8-in range for 5/4 decking, and a wider gap lowers the board count — a 1/4-in gap takes the headline deck from 35 boards to 34. The model counts face screws on straight runs only: hidden fasteners, diagonal and herringbone layouts, stairs, railings, fascia and framing are outside it, and no waste allowance is included — order about 10% over the total. Screw length and gauge follow the board thickness and the manufacturer's directions. This page is a calculation tool, not a building code reference: follow local code and the board manufacturer's span tables for the spacing itself.
A 16 ft by 12 ft deck at 16-in joist spacing with 5.5-in boards needs 700 screws — 35 boards at 20 screws each, 364.58 per 100 sq ft. Rates: 2 screws per joist crossing (engineerfix.com, trexprotect.com); joists = span / spacing + 1, rounded up (chippy.tools); 1/8-in board gap. Source: Bright Side Kit, brightoolbox.com.
20 screws on a 12-ft board at 16-in joist spacing — 10 joists times 2 screws per crossing. At 12-in spacing it is 26, at 24-in spacing it is 14.
700 screws — 35 boards at 20 screws each, 364.58 per 100 sq ft. Order about 10% extra for dropped screws and stripped heads.
16 in on center suits most decking run perpendicular to the joists. Use 12 in for diagonal decking or composite boards, and 24 in for 2x6 decking.
Yes — 2 screws at every joist the board crosses. One screw lets the board pivot and cup; two hold it flat.
364.58 at 16-in spacing with 5.5-in boards, 473.96 at 12-in, 255.21 at 24-in. Wider boards need fewer screws per 100 sq ft — 281.25 at 16-in spacing with 7.25-in boards.
2-1/2-in screws for 5/4 decking, 3-in to 3-1/2-in for 2x decking. See the site's deck-screw-chart for sizes and lengths by board thickness.
In a straight line, about 3/4 in to 1 in from each board edge. Staggering creates uneven pressure and can lead to warping.
Composite boards often need 12-in joist spacing, which raises the count — 910 screws on this deck instead of 700. Many composites also use hidden fasteners instead of face screws; follow the manufacturer's rating.