Building a new deck is one of the highest-return outdoor projects a homeowner can start, yet the estimates contractors hand you can swing by tens of thousands of dollars depending on the material, the footings, and how many stairs and railings the plan hides. This deck cost calculator breaks the job into the four buckets that actually drive the bill — the decking surface, the concrete footings under it, the guard railing on the open sides, and the stair flights — so you can price pressure-treated wood against composite board in seconds and see exactly where your money goes.
Adjust the dimensions and every figure updates instantly. Swap the material, bump the railing length, or add a second stair flight, and the total plus the cost per square foot recalculate before your eyes.
How to Use
- Enter the Deck Width and Deck Depth in feet. Measure the proposed pad on the ground or on blue painter's tape before trusting any contractor's number.
- Pick your Decking Material. Pressure-treated wood is the budget workhorse at roughly $25 per square foot installed; composite (PVC-capped) boards look like wood, last decades, and run closer to $55 per square foot.
- Confirm the Decking Cost per Sq Ft. The default matches the material you chose, but local lumber yards vary — type in the real quote if you have one.
- Set the Footing Spacing. Most building codes require a concrete support footing every 6 to 8 feet along the beams, and 8 feet is the standard DIY and pro default.
- Enter the Footing Cost Each. A concrete pier dug below the frost line usually costs $100 to $200 installed.
- Add the Railing Length — only the open sides. The side nailed to the house needs no guardrail.
- Set the Railing Cost per Foot, then add Stair Flights and their cost each.
The result card shows the deck area, the number of footings required, each cost bucket, the grand total, and the blended cost per square foot — the single number you should compare against contractor bids.
The Deck Cost Formula
Deck pricing is fundamentally area pricing plus structural extras:
Total = (Width × Depth × Rate) + ⌈2(Width + Depth) ÷ Spacing⌉ × Footing Cost + Railing Ft × Railing Rate + Stair Flights × Stair Cost
Where the footing count rounds up because you can't pour a fraction of a pier, and footings are spaced every 8 feet around the support beams. Worked example on a 16 ft × 12 ft (192 sq ft) pressure-treated deck at $25/sqft: decking is $4,800; the 56 ft perimeter calls for 7 footings at $150 = $1,050; 20 ft of railing at $45 = $900; one stair flight at $300. Grand total: $7,050, or about $36.72 per square foot.
Switch that same 192 sq ft footprint to composite at $55/sqft and decking alone jumps to $10,560 — roughly twice the wood bill — even though the footings, railing and stairs barely change. That is why material choice, not size, is where the money actually moves.
Pressure-Treated Wood vs Composite
- Pressure-treated pine: $15–$30/sqft installed. Cheap to build, needs staining every 1–2 years, lasts 10–15 years. Best for tight budgets and rental flips.
- Composite (capped PVC): $40–$65/sqft installed. Never rots, never needs paint, 25-year warranty on most boards. Better long-term value if you plan to stay 10+ years.
A 400 sq ft deck shows the gap clearly: wood lands near $10,000, composite near $22,000 — a $12,000 swing that only makes sense if maintenance avoidance is worth $1,200 a year to you.
Examples
Example 1 — A modest 16×12 backyard deck. Pressure-treated wood at $25/sqft, footings every 8 ft at $150 each, 20 ft of railing at $45/ft, one stair flight at $300. Decking $4,800, footings $1,050, railing $900, stairs $300. Total $7,050 — $36.72/sqft. This is the classic starter deck most contractors bid between $6,500 and $8,500.
Example 2 — A 20×14 composite upgrade. 280 sq ft at $55/sqft = $15,400 in decking; 9 footings = $1,350; 30 ft of aluminum railing at $45/ft = $1,350; two stair flights at $300 = $600. Total $18,700 — $66.79/sqft. Composite decks of this size routinely bid $17,000–$21,000, so the calculator lands right in line.
Example 3 — A zero-budget sanity check. With deck width 0, the area is 0 and the blended cost per square foot falls back to $0, yet footings and railing still price out at $900 — proving that even a "free" pad carries structural costs. Use this to catch contractor quotes that bundle everything into one per-square-foot number and hide the footing work.
FAQ
How much does it cost to build a deck per square foot?
Nationally, a pressure-treated wood deck runs $20–$35 per square foot installed, while capped composite runs $45–$70 per square foot. The all-in number — including footings, railing and stairs — typically lands between $35 and $70 per square foot, which is exactly what this calculator's blended output estimates.
Is composite decking worth the extra cost over pressure-treated wood?
Composite costs roughly twice as much up front but never needs staining or sealing and carries a 25-year warranty. If you plan to live in the home 10 years or more and dislike maintenance, the premium usually pays off; if you plan to sell within 5 years, pressure-treated wood delivers nearly the same home-value lift at half the price.
How many footings does a deck need?
Engineers and building codes require a concrete support footing about every 6–8 feet along the perimeter beams. This calculator divides the deck perimeter by your chosen spacing (default 8 ft) and rounds up, so a 16×12 deck with a 56 ft perimeter needs 7 footings. Always confirm with your local building department, as frost depth drives footing size.
How much does deck railing cost per foot?
Wood railing runs $30–$45 per linear foot installed; aluminum railing $50–$70; cable or glass railing $80–$120. Most decks only need railing on the open sides — the side attached to the house does not — so measure those two sides before pricing.
Do I need a permit to build a deck?
Almost always, for any deck more than 30 inches off the ground. Permit fees typically run $200–$600 and require engineered footing drawings. Skipping the permit can block a future home sale and void your insurance if someone is injured.
How long does a deck last?
Pressure-treated pine lasts 10–15 years if stained on schedule; composite and PVC-capped boards last 25–30 years; aluminum framing underneath lasts essentially forever. The deck boards are the part that wears out — budget for a resurfacing every 15 years even on a high-end build.
What adds the most unexpected cost to a deck?
Retaining walls for sloped yards, stairs longer than four steps (which often need railings and permits), and ground-level deck blocks replaced by frost-depth concrete piers. Each can add $1,000–$3,000 that a per-square-foot estimate alone will never show.
Disclaimer
This deck cost calculator is provided for informational purposes only and does not constitute construction, engineering, or contracting advice. Estimates are based on the inputs you enter and the standard per-square-foot cost model; actual bids vary by region, season, lumber prices, soil conditions, frost depth, and local permit requirements. Always confirm your final design, footing schedule, and budget with a licensed contractor and your local building department before breaking ground.