Deck Calculator
A 12 by 10 foot deck, 5.5 inch boards, 1/8 inch gap, and joists at 16 inches, is 26 boards, 9 joists, 468 face screws, and 234 hidden fasteners.
Last updated . Length and width start in feet. Board width and gap start in inches. Joist spacing starts at 16 inches on center.
Boards are counted along the length. Each board spans the width. Joists run the length, perpendicular to the boards, and are spaced along the width, including both ends.
A fence run: fence material calculator. One stick in board feet: board foot calculator.
Deck boards and joists
Board width is the actual face, 5.5 in for a nominal 6 in board. The gap sits between boards, so the count is (length + gap) ÷ (width + gap), rounded up. Joists run the length, across the boards, and include both ends. Two face screws, or one hidden fastener, per board per joist are planning rates, not a brand.
Results
How the boards and joists are counted
The gap sits between boards, so the board count is (length + gap) ÷ (face width + gap), rounded up. At 12 ft, a 5.5 in face, and a 0.125 in gap, that is 26 boards. Board length is 26 × 10 ft = 260.00 ft. Joists run the length and are spaced across the width: ceil(width ÷ spacing) + 1. At 16 in, 120 ÷ 16 is 7.5, which rounds up to 8 spaces, so the joist line is 9.
Face screws are boards × joists × 2 = 468. Hidden fasteners are boards × joists × 1 = 234. Both rates are planning figures. A nominal 6 in deck board is entered as 5.5 in because the count uses the actual face. This page does not price the lumber.
Joist spacing on the 12 by 10 deck
Boards stay 26. Only the joist and fastener lines move.
| Spacing | Joists | Face screws | Hidden fasteners |
|---|---|---|---|
| 12 in | 11 | 572 | 286 |
| 16 in | 9 | 468 | 234 |
| 24 in | 6 | 312 | 156 |
Worked example
Enter 12 ft by 10 ft, a 5.5 in face, a 0.125 in gap, and 16 in spacing. Leave both fastener rates. Area reads 120.00 ft² · 11.15 m². Boards read 26. Board length reads 260.00 ft · 79.25 m. Joists read 9. Face screws read 468. Hidden fasteners read 234.
Deck questions
How many deck boards for a 12 by 10 deck?
Leave length at 12 ft and width at 10 ft. Board face stays 5.5 in and the gap stays 0.125 in. Area reads 120.00 ft² · 11.15 m². Boards read 26. Board length reads 260.00 ft · 79.25 m. The 5.5 in face is the actual width of a nominal 6 in board. The gap is between boards.
How many joists and fasteners at 16 inches?
Spacing stays 16 in. Joists read 9. They run the 12 ft length and are spaced across the 10 ft width the boards span, so 120 ÷ 16 rounds up to 8 spaces plus the end joist. Face screws read 468. Hidden fasteners read 234. Screws start at 2 per board per joist. Hidden fasteners start at 1 per board per joist. Those are planning rates, not a clip brand.
What if the boards are butted with no gap?
Set the gap to 0. Boards read 27. Board length reads 270.00 ft · 82.30 m. Joists stay 9. Face screws read 486. Hidden fasteners read 243. Area stays 120.00 ft² · 11.15 m². A zero gap uses the 5.5 in face alone.
What does 12 inch joist spacing change?
Choose 12 in OC. Joists read 11. Face screws read 572. Hidden fasteners read 286. Boards stay 26 and board length stays 260.00 ft · 79.25 m. The spacing menu writes 12 into the spacing box and sets the unit to inches.
What does 24 inch joist spacing change?
Choose 24 in OC. Joists read 6. Face screws read 312. Hidden fasteners read 156. Boards stay 26. The deck area does not change when only the joist spacing changes.
What if each board has to span 12 feet?
Set the width to 12 ft and set spacing back to 16 in. Area reads 144.00 ft² · 13.38 m². Boards stay 26. Board length reads 312.00 ft · 95.10 m. Joists stay 10. Face screws stay 520. This count does not reuse offcuts, and it does not add butt joints when a stock board is shorter than the width.
Is this the fence or the board-foot page?
No. Posts, rails, pickets, and gates are the fence material calculator. One board’s nominal size in board feet is the board foot calculator. This page is the deck count: boards along the length, joists at 12, 16, or 24 inches, and the two fastener rates.