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Deck Calculator

Estimate every material you need to build a deck — from decking boards and joists to concrete footings and hidden fasteners. Compare pressure-treated pine and composite decking costs side-by-side, and get a complete material list in seconds. Perfect for ground-level and elevated decks up to 6 feet above grade.

Affects posts and stair estimate

📊 Deck Material Estimate

Deck Area—
Decking Boards Needed—
Joists Needed—
Beam Lumber (2×10)—
Concrete Footings—
Posts (4×4)—
Deck Screws / Fasteners—
PT Pine — Est. Material Cost—
Composite — Est. Material Cost—
Cost per Sq Ft (Selected)—
Includes 10% waste factor on decking and joists. Cost estimates based on national average lumber prices (2026). Actual prices vary by region.

How to Use the Deck Calculator

Measure your planned deck dimensions in feet — length is typically the dimension parallel to the house, width extends outward into the yard. Enter both numbers into the calculator along with your preferences for joist spacing, beam type, and decking material.

Decking boards are calculated using the actual face width of 5.5 inches (a nominal 6-inch "5/4×6" board) plus a 1/4-inch gap between boards for drainage and expansion. The formula divides the deck width in inches by 5.75 inches (board + gap) to determine how many rows you need, then multiplies by the deck length divided by standard board length (typically sold in 12, 16, and 20 ft lengths). A 10% waste factor is added for cuts, knots, and defects.

Joist spacing at 16 inches on center is standard for most residential decks. Use 12-inch spacing if you're installing composite decking (which can sag between wider spans) or if your deck will host heavy loads like hot tubs or large gatherings. The joist count formula is length ÷ spacing + 1 — the "+1" adds the end joist.

Beams and footings: A double 2×10 beam is standard for decks up to 12 feet wide. The calculator assumes beams run perpendicular to joists with support posts every 6–8 feet. Concrete footings are sized based on deck height and local frost depth requirements — the calculator provides a minimum count assuming standard 6-foot post spacing along the beam.

Pressure-Treated vs Composite Decking

Feature Pressure-Treated Pine Composite (Trex, etc.)
Cost per sq ft (materials) $3–6 $8–14
Lifespan 15–20 years (with maintenance) 25–30+ years
Maintenance Annual cleaning, stain/seal every 2–3 years Occasional soap and water wash
Joist spacing required 16–24 in 12 in (or 16 in with special clips)
Splinters / fading Splinters over time, fades to gray No splinters, color-stable (capped composites)

Deck Building Tips

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Frequently Asked Questions

Divide your deck width (in inches) by the board face width plus gap — typically 5.5" + 0.25" = 5.75 inches per board. Then multiply by the number of board lengths needed to span the deck length. For a 12-foot-wide by 16-foot-long deck: 144 inches ÷ 5.75 = 25 rows. If using 16-foot boards, that's 25 boards. If using 12-foot boards, you'll need 50 boards (two per row with staggered joints). Our calculator handles these layout calculations and adds 10% for waste.
For DIY construction: pressure-treated pine runs $15–25/sq ft total (materials + fasteners + footings). Cedar runs $25–35/sq ft. Composite decking runs $35–55/sq ft. Professionally installed, expect $35–60/sq ft for PT pine and $55–100/sq ft for composite. These are 2026 national averages — labor costs vary significantly by region and deck complexity (height, stairs, railings, built-in benches).
16 inches on center is standard for 5/4 decking boards (actual thickness ~1 inch) and works for both PT pine and cedar. Composite decking typically requires 12-inch spacing because it's more flexible and can sag between wider joist bays. If you're using 2×6 decking (actual thickness 1.5 inches), you can go to 24-inch spacing. Always check the manufacturer's span tables — they override any general rule.
Footings support the beam, which runs perpendicular to the joists. A general rule is one footing every 6–8 feet along the beam, plus one at each end. For a 16-foot-wide deck with a beam at the outer edge, you'd typically need 3–4 footings (at 0 ft, 6–8 ft, 12–16 ft). Add a second row of footings if your deck extends more than 12 feet from the house, requiring a mid-span beam. Footing diameter depends on the load but typically 12–18 inches.
Hidden fasteners (clip systems that fasten between boards) give a clean, screw-free surface and are the standard for composite decking. They cost more — about $1–2 per square foot extra — but eliminate screw pops, rust stains, and the need to pre-drill. Face screws are cheaper and faster to install but leave visible fastener heads. For PT pine, many builders still use face screws with a plug system; for composite, hidden fasteners are strongly recommended. Expect about 350 screws per 100 square feet with face-fastening, or 1 clip per board per joist with hidden systems.