How much does it cost to build a deck per square foot?

A pressure-treated wood deck costs $15-$25 per square foot for materials, while composite decking runs $30-$60 per square foot. With professional labor, total installed costs are $25-$45 for wood and $45-$85 for composite. A typical 12x16 deck costs $4,800-$16,000 total.

How many boards do I need for a deck?

Divide your deck's square footage by the coverage area of one board. A standard 5.5-inch wide deck board covers 0.46 sq ft per linear foot. For a 200 sq ft deck with 12-foot boards, you need approximately 37 boards. Add 10-15% for waste and cuts.

What size deck joists do I need?

For most residential decks, 2x8 joists span up to 10.5 feet and 2x10 joists span up to 13.5 feet at 16 inches on center. Use 2x6 joists only for spans under 8 feet. Always check your local building code, as span tables vary by lumber species and grade.

How deep should deck post footings be?

Deck footings must extend below the frost line, which varies by region from 12 inches in the South to 48 inches or more in northern states. Most codes require a minimum 12-inch diameter footing. Check your local building department for the exact frost depth in your area.

Deck Calculator

Estimate decking boards, joists, beams, posts, fasteners, railing materials, and costs for your deck project based on dimensions, material, and design choices.

Deck Length (ft)

Parallel to the house

Deck Width (ft)

Projecting out from the house

Decking Material

Board Size

Board Direction

Joist Spacing (on center)

16" is standard; 12" for composite/diagonal

Deck Height (ft)

Height from ground to deck surface (1-8 ft)

Railing

Required by code if deck is 30"+ above grade

Stairs to Grade

Deck Material List

Decking

Total Deck Area

240 sq ft

20 ft x 12 ft

Deck Boards Needed

5/4x6 x 20 ft boards

Total Board Linear Ft

540 ft

Includes 5% waste

Framing

Joists

2x10 x 20 ft each, 16" OC

Ledger Board

2x10 x 20 ft, pressure treated

Rim Joists

2x10 x 20 ft each

End Caps

2x10 x 12 ft each

Beams

Doubled 2x10, 12 ft span

Posts / Piers

4x4 x 8 ft, 4 beams x 3 posts

Concrete (60 lb bags)

2 bags per pier

Flashing

20 ft

Galvanized or aluminum, at ledger

Railing (3 sides)

Railing Linear Ft

52 ft

3 sides (excludes house side)

Railing Posts

Every 6 ft on center

Rails (linear ft)

104 ft

Top and bottom rails

Balusters

156

4" on center per code

Hardware Shopping List

Item	Qty	Spec
Joist hangers	20	For 2x10 joists
Post bases (Simpson PBS)	12	For 4x4 posts
Ledger lag bolts	15	1/2" x 4" lag bolts
Carriage bolts (beam-to-post)	24	1/2" x 6" with nuts/washers
Deck screws	840	~3 lb boxes
Structural screws/nails	256	3" and 3-1/2" structural
Flashing	20	20 linear ft galvanized
Concrete (60 lb bags)	24	2 bags per pier

Lumber Shopping List

Lumber	Qty	Use
5/4x6 x 20' Pressure-Treated Wood	27 pcs	decking
2x10 x 20' Pressure-Treated	10 pcs	joists
2x10 x 20' Pressure-Treated	1 pcs	ledger board
2x10 x 20' Pressure-Treated	2 pcs	rim joists
2x10 x 12' Pressure-Treated	2 pcs	end caps
2x10 x 12' Pressure-Treated	8 pcs	beams (doubled)
4x4 x 8' Pressure-Treated	12 pcs	posts
4x4 x 8' Pressure-Treated	10 pcs	railing posts
2x4 x 8' Pressure-Treated Wood	14 pcs	top/bottom rails
2x2 x 8' Pressure-Treated Wood	156 pcs	balusters

Estimated Cost (Pressure-Treated Wood)

Low Estimate

$3,600

$15/sq ft installed

Mid Estimate

$4,800

Materials + labor

High Estimate

$6,000

$25/sq ft installed

Code Compliance Notes

*Railing required if deck is 30"+ above grade (IRC R507.1)
*Balusters must be spaced so a 4" sphere cannot pass through (IRC R507.8.3)
*Ledger must be lag-bolted to rim joist, not nailed (IRC R507.2.1)
*Footings must extend below frost line (check local code)

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How to Use This Calculator

Enter your deck dimensions (length and width in feet), select your decking material, board size, and layout direction. Choose joist spacing based on your material's span rating. Set the deck height for accurate post and pier calculations. Toggle railing on to get baluster, post, and rail estimates per building code. Enable stairs if your deck needs steps to grade. The calculator provides a complete material list, hardware summary, and lumber shopping list.

Formula Used

Deck Area = Length x Width. Deck Boards = (Width / (Board Width + Gap)) x Waste Factor. Joists = (Width / Joist Spacing) + 1. Posts = (Beams) x (Posts per Beam). Beams = (Length / 8) + 1. Posts per Beam = (Width / 8) + 1. Screws = Area / 100 x 350. Balusters = Railing Linear Ft x 3 (4 in. on center). Stair Stringers = 3 for 36 in. width + 1 per additional 16 in.

Wood Beam & Joist Designer (NDS)Wall Framing Calculator Stair Calculator

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Disclaimer

This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.