Deck Calculator: Boards, Framing, Footings & Cost

Deck material calculator

Deck length, width and height, joist spacing and decking material (pressure-treated, cedar, composite, PVC or ipe). The result lists every board, joist, post, footing and box of screws.

Deck calculator examples: materials by deck size

The calculator above, run for attached decks 3 ft off the ground with joists 16 in on center and 10% decking waste. Material cost only, at 2026 retail prices — no labor, railings or stairs.

Installed by a contractor, the same decks cost several times the material price — see the deck cost calculator and deck cost per square foot. Resale: the Cost vs. Value 2025 report puts a 16 × 20 ft wood deck addition at $18,263 with 94.9% recouped at sale, and composite at $25,096 with 88.5% (deck ROI calculator).

Deck build essentials

As an Amazon Associate I earn from qualifying purchases.

Top pick

DEWALT 20V MAX Cordless Drill and Impact Driver, Power Tool Combo Kit , Includes 2 Batteries, Charger and Bag (DCK240C2)

Save 38%

$149.00List Price:: $239.00

Check price on Amazon

CAMO EDGEClip Universal Hidden Deck Fasteners Clip (450 ct)

$199.99

Check price on Amazon

FrogTape Pro Grade Deck and Joist Flashing Tape, 1.89 in x 50 Feet, Black

Save 17%

$18.75Typical price:: $22.55

Check price on Amazon

Deck Plus Deck Screws, #10 x 2-1/2in, 365 Pieces,5 Lb Box, Tan

$29.98

Check price on Amazon

Prices and savings as of Oct 10, 2026, 4:35 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.

🎁 Shopping for someone? See our backyard gift guide for deck builders & DIYers.

Deck calculator FAQ

How do I calculate how much decking I need?

Divide the deck width (the direction the boards stack) in inches by 5.75 — a 5.5 inch board plus a 1/4 inch gap — and round up for the number of rows. Multiply rows by the deck length for linear feet, add 10% for waste, and divide by the board length. A 16 × 12 ft deck needs 26 rows, about 458 linear feet, or 29 sixteen-foot boards.

How do I use a decking calculator with gaps?

The calculator above already allows a 1/4 inch gap between 5.5 inch boards (5.75 inches per row). For a wider gap, use the deck board gap calculator; for hidden-clip composite decking, follow the clip's built-in spacing.

How many joists do I need for a deck?

One joist for every 16 inches of deck length plus one: a 16 ft long deck has 13 joists at 16 in on center. Use 12 in spacing for composite boards laid diagonally, and check the joist size against a span table for your species and grade.

How much does it cost to build a deck yourself?

Materials for a 16 × 12 ft pressure-treated deck run about $2,050–$2,630 with the calculator above, or $3,180–$4,080 with composite boards, before railings, stairs and permits. A contractor-built deck costs more — use the deck cost calculator for an installed price.

Does a deck add value to a house?

Most of its cost. The Cost vs. Value 2025 report puts a 16 × 20 ft wood deck addition at $18,263 nationally, returning $17,323 at sale (94.9%), and a composite deck at $25,096, returning $22,199 (88.5%).

What size deck can I build without a permit?

Most US codes based on the IRC exempt only small, low, freestanding decks — typically under 200 sq ft, under 30 inches above grade and not attached to the house. Local rules vary, so check the deck permit guide and your building department before you dig footings.