Deck Material Calculator
Estimate the materials needed to build a deck with this deck calculator. Enter dimensions to calculate boards, supports, and materials required. Ideal for DIY projects and construction planning.
Deck Specifications
Materials Needed
Enter deck dimensions to estimate materials.
How Deck Material Is Calculated
Deck board quantity is calculated by dividing the deck area by the effective coverage of each board. A 6-inch wide board with 1/8" spacing has an effective width of 6.125 inches (6" + 0.125"). Divide deck length by 6.125/12 to find boards needed per row, multiply by the number of rows (deck width ÷ 6.125/12), and add 10–15% for waste from end cuts and defects.
Beyond decking boards, a complete deck project also needs joists (typically 2×8 or 2×10 pressure treated, spaced 16" on center), rim joists, posts (4×4 or 6×6), concrete for footings, post hardware, joist hangers, and fasteners. For an accurate budget, price out all structural components — the decking boards are often only 40–50% of total material cost.
Decking Material Options
Pressure-treated lumber is the most affordable option ($2–4/linear foot) and is code-compliant for ground contact applications, but requires annual sealing and staining to prevent cracking and graying. Cedar and redwood are naturally rot-resistant, more attractive, and run $4–8/linear foot — they still need sealing but hold up better untreated than pine. Composite decking (Trex, TimberTech, Azek) costs $8–15/linear foot upfront but requires little maintenance — no sealing, no staining, no splinters — and typically carries a 25–30 year warranty. For a deck you plan to keep 15+ years, composite often has a lower total cost of ownership than wood despite the higher initial price.
Frequently Asked Questions
How much does it cost to build a deck per square foot?
Material costs typically run $15–25/sq ft for pressure-treated wood decks and $30–45/sq ft for composite decking, not including footings, stairs, or railings. Labor adds $15–30/sq ft if you hire a contractor. A basic 300 sq ft pressure-treated deck runs $9,000–$16,000 installed; the same size in composite runs $15,000–$25,000. Building permits add $200–$1,500 depending on your municipality. DIY labor savings are significant — 40–50% of contractor cost — but permits and inspections are still required in most jurisdictions.
Do I need a building permit for a deck?
In most jurisdictions, yes — if the deck is attached to the house, over a certain height (usually 30"), or over a certain size (commonly 200 sq ft). Permits ensure your footings, posts, and connections meet structural and safety codes. Building without a permit can create problems when you sell the home (discovered during inspection), when making insurance claims, or if the deck fails and injures someone. Contact your local building department before starting — the permit process is straightforward for standard decks and the inspection provides peace of mind.
How far apart should deck joists be spaced?
Standard joist spacing is 16" on center for most decking materials. For composite decking installed at a 45-degree angle (diagonal), reduce to 12" on center to prevent flexing. Some thicker composite products allow 24" spacing — check the manufacturer's installation guide. Wider spacing saves on joist material but reduces stiffness and limits your decking options. Joists should be sized for your deck span: 2×8 joists can typically span up to 12 feet, 2×10 up to about 16 feet, with proper sizing based on span tables in your local building code.
How to Use This Calculator
- Enter your deck length and width in feet.
- Enter the board width in inches (common sizes are 6" or 5.5" nominal; actual widths are typically 5.5" and 5.25" respectively).
- Enter the gap spacing between boards in inches (1/8" is the standard gap for wood; composite boards vary by manufacturer).
- Click Calculate to see deck area, total linear feet of decking needed, and approximate board count.
- Add 10–15% to the board count for waste from end cuts and defects when placing your lumber order.
Worked Example
You are building a 16 ft × 12 ft deck using 6-inch boards with standard 1/8-inch gaps.
Deck area
16 × 12 = 192 sq ft
Effective board width (6" + 0.125")
6.125" = 0.510 ft
Boards spanning the 16 ft length
16 ÷ 0.510 = 31.4 → 32 boards
Total linear feet (32 boards × 12 ft)
384 linear feet
Disclaimer: Results are estimates. Actual material quantities depend on board species, actual vs. nominal dimensions, installation pattern, and waste from cuts. Construction requirements — including permits, structural calculations, and code compliance — vary by jurisdiction. Verify all specifications with a qualified contractor or building professional before purchasing materials or beginning construction.