Deck Cost Calculator
Build an itemised estimate for a new deck — footings and posts, framing, decking with waste, fasteners, railing by the foot, stairs by the step and labour scaled for height — from prices you collect locally, so the total fits your lumber yard and your contractors rather than a national average.
How to use this calculator
- Size and height first. Length runs along the house, width out from it. Height decides two expensive things: whether code requires a guard rail (above 30 in) and how much slower the crew works on a tall frame.
- Attached or freestanding. A ledger-mounted deck needs one beam and railing on three sides; a freestanding deck needs a second beam, twice the posts and footings, and railing all the way round. Some jurisdictions and some house constructions push you to freestanding.
- Count the steps. Roughly one step per 7½ in of height — a 24 in deck needs three risers. Stairs are priced per step because each step is a full width of treads, risers and stringer work, and railing on stairs adds to the per-step figure.
- Replace the placeholder prices. The lumber yard gives you decking and framing prices; divide a full takeoff by the deck area to get your per-square-foot figures, or use the yard’s own per-square-foot estimate. Ask contractors to itemise labour, railing and stairs separately — bids that lump everything into one number cannot be compared.
The formula
The estimate follows the load path of the deck — footings, frame, surface, then what stands on it — and prices each layer by its natural unit:
| Line | Quantity | Cost |
|---|---|---|
| Footings | posts = (floor(length ÷ 8) + 1) × beams | posts × price per footing |
| Framing | area (joists = floor(length × 12 ÷ 16) + 1) | sq ft × rate |
| Decking | area × (1 + waste) | sq ft × rate |
| Fasteners | area | sq ft × rate |
| Railing | attached: length + 2 × width; freestanding: full perimeter | linear ft × (materials + labour) |
| Stairs | steps | steps × installed price per step |
| Labour | area | sq ft × rate × height factor |
| Demolition, permit | area / flat | optional lines |
| Contingency | — | subtotal × percentage |
The height factor (1.15 elevated, 1.35 second storey) reflects ladders, staging, taller posts and bracing; it multiplies only the framing and decking labour. Railing and stairs carry their own labour rates because they scale with feet and steps, not with deck area — which is why a small high deck can cost more per square foot than a large low one.
Worked example
A 16 × 12 ft deck attached to the house, 30 in to 6 ft above grade, railing on the three open sides, three steps, no demolition, with the placeholder prices:
- Area: 16 × 12 = 192 sq ft; joists at 16 in: floor(192 ÷ 16) + 1 = 13; posts along one 16 ft beam: floor(16 ÷ 8) + 1 = 3
- Footings: 3 × $60 = $180.00; framing 192 × $6.00 = $1,152.00
- Decking: 192 × 1.10 = 211 sq ft × $4.50 = $950.40; fasteners 192 × $0.50 = $96.00
- Railing: 16 + 2 × 12 = 40 lf; materials 40 × $30 = $1,200.00; labour 40 × $20 = $800.00
- Stairs: 3 × $120 = $360.00
- Labour: 192 × $12 × 1.15 = $2,649.60
- Subtotal $7,388.00; contingency 10% = $738.80; estimated total $8,126.80, or $42.33 per sq ft
Railing is $2,000 of that — more than the decking boards — which is why a ground-level deck that needs no guard costs so much less per square foot, and why composite railing systems move a bid more than composite boards do. These are the defaults in the form above; press Calculate and the numbers match.
Decking materials, relative to pressure-treated pine
| Decking | Board cost, roughly | Notes |
|---|---|---|
| Pressure-treated pine | 1.0× (baseline) | Cheapest; needs sealing every 1–2 years; shrinks and checks |
| Cedar or redwood | 1.5–2.5× | Naturally rot-resistant; still needs finish to keep its colour |
| Composite (capped) | 2.5–3.5× | No sealing; 16 in joists or less; hidden fasteners |
| PVC | 3.5–4.5× | Lightest, most stable; the premium tier |
| Hardwood (ipe etc.) | 3–5× | Very hard, very heavy; specialist fastening |
Because boards are about a quarter of a typical bill, a 3× board price raises the whole deck by roughly half, not three times. Change the decking input above to see it on your deck.
What moves a deck quote
- Height. Guard rails, longer posts, bracing, staging and stairs all arrive together once a deck leaves the ground.
- Railing. Priced by the foot and often 20–30% of the job; composite and metal systems multiply it.
- Frost depth. Footings to 42 or 48 in cost far more than 12 in pads; some regions allow helical piers or precast footings instead.
- Ledger and house connection. Flashing, lag or through-bolts, and sometimes siding repair; a freestanding deck avoids it at the cost of a second beam.
- Shape. Angles, curves, multiple levels and picture-frame borders add cuts, waste and hours.
- Permit and inspections. Footing, framing and final inspections are normal; the fee varies widely.
For the takeoff behind the framing and decking lines, the deck calculator counts boards, joists and screws, the stair calculator sizes the risers and treads, and the 16 × 12 deck walkthrough follows this same deck from footings to boards.
Frequently asked questions
How much does a deck cost per square foot?
It depends on your region, the height, the railing and the boards, so this page asks for your local prices rather than quoting one figure. With the placeholder rates in the form, a 16 by 12 foot pressure-treated deck with railing and three steps comes to just over 40 dollars per square foot including contingency; a ground-level deck with no railing is far less, and composite boards and railing raise it by half or more.
Why does a small high deck cost more per square foot than a big low one?
Because railing and stairs are priced by the foot and by the step, not by the area, and a tall deck needs both plus longer posts and slower work. Spread over a small area those fixed costs dominate. Doubling the area of a deck rarely doubles its price.
Is composite decking worth the extra cost?
Composite boards cost roughly two and a half to three and a half times pressure treated pine, but boards are about a quarter of a deck bill, so the whole deck rises by around half. In exchange you skip sealing every year or two for the life of the deck. Over fifteen or twenty years the maintenance saving usually covers the difference; on a short horizon it does not.
Do I need a permit to build a deck?
Almost always if the deck is attached to the house, more than 30 inches above grade, or larger than the small exemption many codes allow for detached ground-level decks. Expect footing, framing and final inspections. Enter the fee in the permit line and check with your building department before pricing anything.
How many footings does a deck need?
One under every post. Posts along a beam are commonly no more than 8 feet apart, so a 16 foot beam needs three posts, and a freestanding deck with two beams needs six. Beam size, post spacing and footing depth depend on the joist span, the load and the frost line, and are set by code.
Guides
- What Drives the Cost of a Deck?
- Composite vs Wood Decking: What the Premium Really Buys
- Do You Need a Permit to Build a Deck? Code Basics
Related calculators
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