Deck Calculator

Enter the deck dimensions, board type, and joist spacing to estimate the number of decking boards, joists, and fasteners needed for a client deck. Includes a 10% waste factor. Results are approximate and intended for planning purposes only — always confirm final specifications against the relevant building code.

Deck Length

Deck Width

Decking Material

Board Length

Joist Spacing

Deck Layout

Results

Deck Area

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Decking Boards (incl. 10% waste)

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Joists

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Joist Length

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Deck Screws (approx.)

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How to Calculate Deck Materials

1
Measure the deck area
Measure the planned length and width of the deck in feet. For L-shaped or multi-level decks, estimate each section separately and add the results together.
2
Choose the decking type
Select the decking material. Pressure-treated pine is typically the most affordable, cedar offers natural rot resistance, composite is low-maintenance, and ipe is among the most hard-wearing.
3
Review the board count
The calculator provides the number of decking boards (with 10% waste), joists based on your spacing selection, and an estimate for deck screws.
4
Plan the framing
Joists run perpendicular to deck boards. Standard spacing is 16 inches on center for most materials, or 12 inches for composite decking to prevent sagging.

Pro Tips

Run deck boards parallel to the longest dimension and perpendicular to joists for the best appearance and structural support.
Use 16-inch on-center joist spacing for wood decking and 12-inch spacing for composite to prevent flex and sagging between joists.
Add 10% extra decking boards for cuts, waste, and warped boards that can't be used — our calculator includes this automatically.
Hidden fastener systems give a cleaner look than face screwing and reduce the chance of splitting, especially with hardwood decking.
Deck boards can cantilever past the outer joist by up to 1/4 of the joist spacing (e.g., 4 inches with 16-inch OC joists).
Check local building codes for railing requirements, post footings, and maximum deck height before finalising the design — figures from this estimator are for planning only.

Frequently Asked Questions

How many deck boards do I need?

Divide the deck width (in inches) by the board width (typically 5.5 inches for a standard 2×6) to get rows, then multiply by the number of board lengths needed to span the deck length. Add 10% for waste.

What is the standard joist spacing for a deck?

16 inches on center is standard for pressure-treated and cedar decking. Use 12-inch spacing for composite decking or if your local code requires it. 24-inch spacing is only acceptable for very thick lumber (2-inch+).

Is composite decking worth the extra cost?

Composite decking costs 2-3x more upfront but requires no staining, sealing, or replacement. Over 20 years, total cost is often similar to wood when you factor in maintenance. Composite also won't splinter or rot.

How many screws do I need for a deck?

Plan for approximately 3–4 screws per square foot of decking, depending on joist spacing. At 16" OC spacing, roughly 3.5 screws per sq ft; at 12" OC, about 4 per sq ft. A 200 sq ft deck at 16" OC needs about 700 screws. Use stainless steel or coated deck screws rated for your decking material.

How far can deck boards span without support?

Standard 5/4 deck boards can span up to 16 inches between joists. 2×6 boards can span up to 24 inches. Composite boards typically require 16-inch maximum spans, and some require 12-inch spans — always check manufacturer specs.

Results are approximate and intended for planning purposes only. Material densities, coverage rates, and quantities are estimates that may vary based on actual conditions, product specifications, and installation methods. Always consult a professional for final specifications.

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