How many deck boards for a 8x12 deck?
You need 18 deck boards at 12 ft long.
That is 18 rows across the 8 ft span, or 216 linear feet. Buy 238 linear feet to cover the usual 10% for cuts and defects.
Where that number comes from
A standard 5/4x6 or 2x6 deck board is 5.5 in wide once milled, not 6 in. Add the 0.125 in drainage gap between boards and each row covers 5.625 in of deck.
- 8 ft across × 12 = 96 in to cover
- 96 ÷ 5.625 = 17.1 rows, rounded up to 18
- 18 rows × 12 ft long = 216 linear feet
- Add 10% for cuts and culls = 238 linear feet
Boards run the length of the deck here, so the 12 ft dimension sets board length and the 8 ft dimension sets how many rows you need. Running them the other way swaps the two numbers.
Change the numbers
What else the frame needs
- Joists at 16 in on centre: about 10 for a 12 ft run.
- Footings: roughly 6 for a deck this size, depending on beam layout and frost depth.
- Deck screws: around 480 — two per board at every joist crossing.
Joist and footing counts vary with span tables, beam placement and local frost depth. Treat them as a shopping estimate, not a structural design, and check your local code before you build.
Getting it right
- Measuring the frame, not the decking. Decking usually overhangs the rim joist by an inch or so on open sides. Measure the surface you intend to cover.
- Buying nominal widths. A "6 inch" board is 5.5 in. Sizing off 6 in leaves you roughly 9% short — on this deck that is about 19 linear feet missing.
- Skipping the gap. Boards need the 0.125 in gap to drain and to move with humidity. Butting them tight traps water and cups the boards.
- Ordering exact. Ten percent covers bowed boards, knots and cut-offs. It is cheaper than a second delivery.
Other deck sizes
Deck calculator for any size, or all calculators.