Enter the total square footage of your deck surface. If your deck is 12×16, that's 192 sq ft. Select your board width, length, joist spacing, and material type. The calculator gives you the number of boards you need (with 10% waste built in for cuts), total linear feet of decking, fastener count, and a material cost estimate.
For a simple rectangular deck, multiply length × width. For L-shaped or multi-level decks, break the area into rectangles and add them up. Don't subtract for stairs — those need decking too, usually calculated separately.
Pressure Treated Pine is the most popular and affordable option. It's chemically treated to resist rot and insects. Expect to pay $2–3 per sqft installed. It needs staining or sealing every 2–3 years and lasts 15–20 years with proper maintenance. Downsides: it can warp, split, and check over time.
Composite Decking (Trex, TimberTech, etc.) is made from a blend of wood fibers and recycled plastic. It runs $6–9 per sqft installed but requires virtually no maintenance — no staining, sealing, or sanding. It lasts 25–50 years, won't splinter, and comes in a wide range of colors. The trade-off: higher upfront cost and it gets hotter in direct sun than wood.
Western Red Cedar is a natural wood option with built-in rot and insect resistance. At $3.5–5 per sqft installed, it's the middle-ground choice. Cedar is beautiful, smells great, and is naturally stable — but it still needs regular sealing to maintain its color (otherwise it grays). Lifespan: 15–25 years with maintenance.
Joist spacing affects both structural integrity and how your decking performs over time. Here's when to use each:
A 12×12 deck is 144 sq ft. Using standard 5.5" boards at 12 ft length, you need about 22 boards exactly — or 25 boards with 10% waste for cuts. If you use 16-ft boards instead, you'd need about 17 boards (19 with waste) but you'd have more offcuts to work with.
Pressure treated if budget matters most — it's proven and affordable but needs staining every 2–3 years. Composite if you don't want to think about maintenance — it costs 2–3x more up front but lasts decades with zero sealing. The break-even point is usually around 8–10 years when you factor in staining costs and your time.
16 inches on center is the standard for residential decks with perpendicular 5.5" boards. Use 12" for diagonal layouts or composite. 24" is only for thick (2×6) wood boards — check your local code.
10% is standard for a rectangular deck with perpendicular boards. Bump to 15% for diagonal (45°) layouts. For complex shapes with lots of notching around posts or railings, go 15–20%. Our calculator includes 10% by default.
Plan on 2 screws per joist crossing. A 12-ft board on 16" centers hits 10 joists — that's 20 screws per board. Always buy 10–15% extra screws. Stripped heads and cammed-out bits happen more than you'd think.