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MaterialCalc — Deck Cost Calculator

Estimate prepared 09/01/2026. Estimates only; verify against your plans before ordering.

Deck Cost Calculator

The dimension the joists span.

Over 30 in and the code wants guardrails.

%

Result

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Decking is the part people price, and it is rarely half the bill. Framing, posts, footings, hangers, fasteners and railing carry the rest, and railing alone can be a fifth of the total on a small deck. This builds the whole material list from your dimensions and prices pressure-treated, composite and cedar against each other.

Assumptions used

These are the numbers behind the result. Where one of them is soft, the cost range widens rather than pretending to a precision the data does not have.

Lumber waste allowance
0.1

Cut-offs, crooked stock and the boards you set aside.

Standard industry overage — Industry standard, varies by supplier, checked 09/01/2026

Concrete waste allowance
0.1

Covers spillage, over-excavated holes and forms that bulge. Footings dug by hand run higher than forms.

Standard industry overage — Industry standard, varies by supplier, checked 09/01/2026

Deck board coverage width
5.5 in

A nominal 5/4x6 or 2x6 board covers 5.5 in. Gaps come out of the waste allowance.

Home Depot / Lowe's published product data — Published product data, checked 09/01/2026

Gap between deck boards
0.1875 in

Drainage and expansion. Composite wants a wider gap than wood — check the maker.

Trex and TimberTech installation guides — Industry standard, varies by supplier, checked 09/01/2026

Deck joist spacing
16 in o.c.

Composite decking laid diagonally usually requires 12 in instead.

International Residential Code (2021) — Published product data, checked 09/01/2026

Deck beam post spacing
8 ft

IRC deck provisions (DCA 6) — Industry standard, varies by supplier, checked 09/01/2026

Deck screws per square foot
3.5 screws/ft²

Fastener manufacturer coverage tables — Industry standard, varies by supplier, checked 09/01/2026

Prices verified 09/01/2026 (US national average, big-box retail shelf price and regional ready-mix quotes). Regional adjustment: Blended from RSMeans city cost index bands and BLS construction wage differentials.

The formula

Board rows = deck width ÷ (board coverage + gap), rounded up; boards = rows × lengths needed per row. Joists = (deck length ÷ 16 in) + 1, each spanning the width. Posts sit at 8 ft centers along the beam, one footing each. Railing covers the perimeter minus the house side.

Worked examples

16x12 pressure-treated deck, 36 in high

Deck length: 16 Deck width: 12 Height above grade: 36 Decking material: pt Waste: 10

192 square feet, about 27 boards and 14 joists on 3 posts. Guardrails are required at this height, and they are a significant slice of the total.

Same deck in composite

Deck length: 16 Deck width: 12 Height above grade: 36 Decking material: composite Waste: 10

Identical framing, roughly triple the decking cost, and hidden fasteners instead of screws. The comparison table shows the gap directly.

20x14 ground-level deck, 12 in high

Deck length: 20 Deck width: 14 Height above grade: 12 Decking material: pt Waste: 10

280 square feet with no guardrail requirement below 30 in. Dropping the railing takes a real bite out of the cost per square foot.

Choosing materials

  • Decking is typically 40 to 55% of the material cost on a pressure-treated deck and 60 to 70% on a composite one. That is why the material choice moves the total more than the size does over a modest range.
  • Joist tape over every joist top is the highest-value $40 you will spend. Water sitting in screw holes is what rots a deck frame, and tape stops it.
  • Use hot-dipped galvanized or stainless fasteners with pressure-treated lumber. Modern treatment chemicals eat plain zinc, and the failure shows up as loose boards in about five years.
  • Railing costs run $30 to $60 per linear foot installed. On a 12x16 deck that is 40 ft of railing, which is often more than the framing underneath it.
  • Footings go below the frost line, and every jurisdiction inspects them before you pour. Building the frame first and hoping is the most expensive mistake on this list.

Common questions

How much does a deck cost per square foot?

Materials alone typically run $15 to $25 per square foot for pressure-treated and $30 to $45 for composite. Built by a contractor, expect $40 to $60 for pressure-treated and $60 to $90 for composite, with height and railing pushing it higher.

Is composite decking worth the extra cost?

It costs roughly three times as much as pressure-treated up front and needs no sealing or staining. Over eight to ten years the maintenance saving closes the gap. If you plan to sell before then, pressure-treated is the better financial choice.

What is the biggest hidden cost in a deck?

Railing and footings. Railing runs $30 to $60 a linear foot installed and is easy to leave out of a mental estimate. Footings need excavation, inspection and concrete, and on rocky or deep-frost sites they can cost more than the framing.

How far apart should deck joists be?

Sixteen inches on center is standard for wood decking laid perpendicular to the joists. Composite decking laid diagonally usually needs 12 in, and some composite products require 12 in even for straight installation — check the manufacturer.

Do I need a permit to build a deck?

Almost always, and especially for anything attached to the house or more than 30 in above grade. The inspection sequence usually runs footings, framing, then final, and starting without one can mean tearing the deck out.

What size joists do I need?

It depends on span. 2x8 joists at 16 in on center span roughly 12 ft in southern pine; 2x10 gets you to about 15 ft. Span tables in the IRC deck provisions give the exact figures for your species and spacing.

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