Deck cost calculator: estimate boards, joists & total price
How to estimate deck materials, framing, concrete, and total cost — formulas plus US average pricing for wood and composite decking in 2026.
April 28, 2026 · 5 min read
Building a deck looks simple — until you start pricing boards, joists, fasteners, and concrete. Here's how to estimate what you actually need (and what it actually costs) without any nasty surprises at the lumber yard.
Step 1 — Measure your deck
Length × width = square footage. A typical 12 ft × 16 ft deck is 192 sq ft. Write it down — every other number flows from this one.
Step 2 — Calculate decking boards
Standard formula:
boards = (deck sq ft / board sq ft) × 1.10
The 10% covers waste from cuts and bad boards. A 5/4" × 6" × 12 ft board covers about 5.5 sq ft. For a 192 sq ft deck: ~38 boards.
Step 3 — Joists & framing
Joists usually run 16" on center. For a 12 ft × 16 ft deck framed across the 12 ft span:
- Joists: 12 × (16 / 1.33) ≈ 13 joists
- Rim joists: 2 × 16 ft + 2 × 12 ft
- Ledger board: 16 ft against the house
Step 4 — Posts, footings & concrete
Posts every 6–8 ft along the beam. Each footing typically needs 1–2 bags of fast-setting concrete. A 12 × 16 deck usually has 4–6 posts.
Smart Decking Calculator is also a free Android app on Google Play now, so you can run the numbers on your phone while you're standing in the backyard.
Material cost (rough US averages, 2026)
- Pressure-treated pine: $15–$25/sq ft installed
- Cedar: $25–$35/sq ft installed
- Redwood: $30–$45/sq ft installed
- Composite (Trex, TimberTech): $30–$60/sq ft installed
- Tropical hardwood (ipe): $40–$70/sq ft installed
So a 192 sq ft pressure-treated deck = roughly $2,900–$4,800. Composite on the same footprint = $5,800–$11,500.
Don't forget
- Stairs ($150–$300 per step installed)
- Railings ($30–$60/linear ft)
- Hidden fasteners (composite decks)
- Permit fees — most cities require one for any deck over 30" off the ground
- Stain or sealant (wood decks need it every 2–3 years)
Composite vs wood — the real math
Composite costs 2–3× more upfront but lasts 25+ years with zero refinishing. Pressure-treated pine is cheap up front but you'll spend ~$200–$400 every couple of years staining it. Over 20 years the lifetime cost is closer than you'd think.
Pricing it on an iPhone? Contractor estimate app for iPhone runs this deck through the deck calculator inside Roofing Calculator & Estimator, then turns it into a PDF quote.
Counting the small parts too? Our free home-project calculators for fall roundup links new joist tape, joist hanger and deck blocking calculators, plus tools for the roof, fence and attic.
Want the count on your phone? Our deck calculator app guide compares the free deck calculator apps for Android, iPhone and the web against a 12x16 worked example.
