Deck Cost Calculator

How much does it cost to build a deck? Start with the materials. This deck cost calculator turns length, width, and a material choice into a board count, a joist count, and a 2026 US materials cost range. It is also a deck material calculator: the same inputs produce a shopping-list style takeoff you can take to a lumberyard.

Numbers are materials only — decking and joists, not labor, railing, stairs, or permits. Treat the range as a national average, then add local tax and about ±15% for your market.

Deck layout

Joist spacing (in o.c.)

On-center along the length. Composite is limited to 16 in o.c.

Materials cost (2026 US average)

How these numbers were counted

Shopping list

How this deck material calculator counts boards and joists

Board count is the number of rows that cover the width, times the number of stock lengths that cover the run, plus waste, then rounded up.

rows    = ceil( width_in / (face_in + gap_in) )
courses = ceil( length_ft / board_length_ft )
boards  = ceil( rows × courses × (1 + waste) )

Face width is the actual board, not the nominal size. A 5/4×6 is 5.5 in. across, not 6.

Deck board face width plus gap used to count rows board face gap face width gap row pitch = face + gap

Joists sit on-center along the deck length, plus one for the far rim even when the last bay is short.

joists = ceil( length_in / spacing_in ) + 1

Default spacing is 16 in. on center. Composite decking: do not go wider than 16 in. o.c. or most warranties are void. If spacing is set past 16 in. on composite, the calculator clamps it to 16 in. and shows a warning.

Materials cost is square footage times a 2026 US band (materials only):

Material Materials $/sf (2026 US)
Pressure-treated $8–$12
Cedar $12–$18
Composite $18–$25 
low  = sqft × band_low
high = sqft × band_high

Local retail often lands about ±15% of this range.

Worked example (must match the live widget)

12 ft × 16 ft, pressure-treated, 5.5 in. face, 1/8 in. gap, 16 ft boards, 16 in. o.c., 10% waste. Boards run the 16 ft side; joists span 12 ft and are spaced along 16 ft. Length = 16, width = 12.

How much does it cost to build a deck?

This calculator prices decking and joists. That is the materials bill, not a contractor quote.

Installed cost is higher. Labor is often about as much as the materials, sometimes more. Railing, stairs, footings, and a permit are separate lines, and none of them are in the range above. Published 2026 guides that quote an installed price sit well above these materials bands. We do not estimate labor. For a contractor total, get three local bids.

If you are building it yourself, use the shopping list. Plan on fasteners and a little extra waste on top of the board and joist counts.

Pressure-treated, cedar, or composite

Material Gap Max joist spacing Waste default Materials $/sf Maintenance
Pressure-treated 1/8 in. 16 in. o.c. typical 10% $8–$12 Stain every few years
Cedar 1/8 in. 16 in. o.c. typical 10% $12–$18 Oil or stain
Composite 3/16 in. 16 in. o.c. (warranty) 12% $18–$25 Wash only

Composite offcuts usually cannot be returned, which is why the default waste is higher. Brand names (Trex, Fiberon, TimberTech) are examples, not filters. This tool is not locked to one retailer.

Deck cost calculator FAQ

How many deck boards do I need?

Divide the deck width in inches by face width plus gap. That is the row count. Divide deck length by the stock board length for courses. Multiply, add waste (10% straight wood, 12% straight composite), and round up. The calculator does this from the length and width you enter.

How do you count joists?

Joists are spaced on-center along the length, then one extra closes the rim: ceil(length_in / spacing_in) + 1. At 16 in. o.c. on a 16 ft run that is 13 joists. A 10 ft run at 16 in. o.c. is 9, not 8. This is a count, not a span check. Have your lumber species and size checked against local code.

What waste factor should I use?

Use 10% for a straight pressure-treated or cedar layout and 12% for straight composite (composite offcuts usually cannot be returned). Picture-frame or diagonal layouts need more; those patterns are not in this calculator yet. You can raise the waste field if your deck has a lot of cuts.

How much does it cost to build a deck in 2026?

Materials for the walking surface and joists typically run about $8–$12 per square foot in pressure-treated, $12–$18 in cedar, and $18–$25 in composite, as a 2026 US average. Labor, railing, stairs, and permits sit on top of that. This page estimates materials only. For a contractor total, compare three local bids.

Does this include labor, railing, or stairs?

No. The cost range is decking and joist material. Railing, stairs, footings, fasteners, tax, and labor are not in the total. The shopping list is a starting takeoff, not a full bill of materials.

Do composite boards need different spacing?

Yes. Composite wants a 3/16 in. gap (thermal movement) and joists no farther than 16 in. on center if you want the warranty. The calculator switches both defaults when you pick composite and clamps joist spacing to 16 in. o.c. and shows a warning.

Is a 12×16 a typical deck size?

Yes. 12×16 is 192 square feet and is one of the most-built rectangular sizes in the US — large enough for a table and chairs, still a common DIY footprint. Plug those dimensions in above to see boards, joists, and the materials range.

Can I use this for a permit or engineering drawing?

No. This is a materials estimator for a rectangle. It is not a structural design, not IRC span verification, and not a permit plan. Check with your local building department (AHJ) before you build. Most attached decks and any deck over 30 in. above grade need a permit.