Deck Calculator,
materials, framing & cost estimated.

Deck building guide

How to read this estimate — and what to verify with your local code.

Joist spacing: the foundation of a stiff deck

Joists are the horizontal floor members that carry the decking. Their spacing — measured center-to-center, abbreviated OC — controls how stiff the finished deck feels underfoot and how thick your decking can be. The three standard residential options:

• 12″ OC — Use this for thinner 5/4 × 6 boards run diagonally, for very heavy point loads (hot tubs, planters, outdoor kitchens), or to absolutely eliminate any springy feel. You'll need roughly 33% more joist material than a 16″ layout.
• 16″ OC — The default for residential decks. Works with every common board size, satisfies most building codes for typical residential loads, and is what 95% of contractors quote. This calculator defaults to 16″ for that reason.
• 24″ OC — Only acceptable with full 2× decking (2×6 or thicker). Saves on framing material but the deck will feel less rigid. Not allowed for 5/4 boards under most codes.

The American Wood Council's prescriptive deck guide DCA-6 publishes detailed joist span tables by species and grade. A 2×8 Southern Pine joist at 16″ OC can span about 13'1″; a 2×10 stretches to about 16'6″. Always check the current edition for your region — span limits tighten in snow-load zones.

Post spacing & footing rules

Posts (and the footings under them) support the beams that carry the joists. The two key rules:

• Posts every ≤ 8 feet along each beam. Longer spacings require larger beams and become exponentially more expensive. 6' spacing is more conservative for heavier decks. This calculator uses 8' max spacing plus an end post on each side of every beam.
• Footings must extend below the local frost line. The frost line ranges from ~12″ in the deep South to 60″+ in the northern Midwest. If a footing sits above frost depth, freeze/thaw cycles will heave the deck out of level over time. Your local building department publishes the required minimum depth.
• 10″ or 12″ diameter is standard. For a typical residential deck supporting normal pedestrian loads, a 10″ diameter footing at the proper depth carries plenty of load. Heavier decks, soft soils, or hot-tub loads may require 12″ or engineer-designed pads.

Material comparison: PT pine vs. cedar vs. composite vs. PVC

The four main residential decking materials have very different cost, maintenance, and lifespan profiles. The estimates below include all-in materials — decking, framing, fasteners, and concrete — based on 2026 national averages.

• Pressure-Treated Pine ($15–35/ft²) — The budget standard. Chemically treated southern yellow pine resists rot and insects for 15–25 years. Requires stain or sealer every 2–3 years. Will check, warp, and splinter without maintenance. The cheapest way to build a deck and still by far the most common in the US.
• Cedar ($25–50/ft²) — Naturally rot-resistant Western Red Cedar has a beautiful warm tone and a long traditional aesthetic. Softer than PT (dents easily), still needs sealing every 2–3 years to preserve color, and not always available in all regions. 20-year expected lifespan with proper care.
• Composite ($30–60/ft²) — Wood flour bonded to polymer resin. Brands like Trex, TimberTech, and Fiberon dominate. No painting, no staining, no splinters — just rinse with a hose. 25-year minimum warranties from major brands; real-world lifespan can be 30+ years. Heavier than wood, so framing spacing is the same as PT.
• PVC / Cellular ($40–80/ft²) — Pure synthetic. The premium choice. Won't rot, fade, or absorb moisture; stays cooler under sun than dark composites. Lightweight (easier to handle), but expensive. Best for poolside and saltwater environments.

Why a waste factor matters

The base board count assumes every board is used at full length with zero offcuts. Real construction never works that way. A straight rectangular pattern still produces 5–10% waste from end cuts, board defects, and saw blade kerf. Diagonal patterns push that to 15% because every board has an angled offcut at each end. This calculator applies 10% waste to straight layouts and 15% to diagonal — order the rounded-up quantity to avoid an extra trip to the lumber yard.

Fasteners: face screws vs. hidden clips

Face-driven deck screws are the budget option — 2 screws per board per joist crossing, typically 2½″ to 3″ exterior-grade. A 16 × 12 deck needs about 1,500 screws (≈ 5 lb). Pre-drilled or coated heads prevent rust streaks. Visible from above unless you plug the holes.

Hidden-clip systems (Camo, Tiger Claw, Trex Hideaway) edge-fasten the boards, leaving a clean surface with no visible fastener heads. Material cost is higher (~3–5× face screws), installation is slower, but the finished look is what sells $50,000+ decks.

Concrete for footings

The volume of concrete needed depends on hole geometry: a cylinder of diameter d and depth h contains π × (d/2)² × h of concrete. A 10″ diameter × 36″ deep footing holds roughly 0.06 yd³ (1.6 ft³). Standard 60-lb bags yield about 0.45 ft³ mixed; 80-lb bags yield about 0.60 ft³. Always order at least 10% extra to handle spillage, hole-bottom irregularities, and the inevitable mismeasured footing. For larger pours, our Concrete Calculator handles slab, column, and footing geometry with multiple bag options.

Beam sizing — a quick heuristic

This calculator suggests a beam size based on the joist span and the number of beams. The doubled-2× sizes — (2) 2×6, (2) 2×8, (2) 2×10, (2) 2×12 — are the residential standard, fastened face-to-face with structural screws or through-bolts. The suggestion follows the general DCA-6 spans for two-ply beams of Southern Pine #2, but always verify with current span tables for your species, grade, and snow load. A professionally engineered LVL or PSL beam may be cheaper and lighter for very long spans.