MaterialCalc — Deck Cost Calculator

Estimate prepared 10/31/2026. Estimates only; verify against your plans before ordering.

Deck Cost Calculator

Enter your measurements and get both numbers: how much material the job takes, and what it costs in your state.

60Calculators

09/01/2026Prices checked

7assumptions shown

Live estimate—

01 / 03Measurements

How big is it?

Measure to the outside. Round to the nearest half foot — nothing on a job site is exact.

Deck length

Deck width

The dimension the joists span.

Height above grade

Over 30 in and the code wants guardrails.

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
Concrete waste allowance: 0.1
Deck board coverage width: 5.5 in
Gap between deck boards: 0.1875 in
Deck joist spacing: 16 in o.c.
Deck beam post spacing: 8 ft
Deck screws per square foot: 3.5 screws/ft²

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.