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Deck Calculator

Boards, joists, screws — order once, build once.

Deck material math is coverage math: each 5.5-inch board with a 1/8-inch gap covers 5.625 inches of width, rows multiply by length for total linear feet, and joists follow spacing rules plus one for the rim. This calculator runs the full count — boards with 10% waste, joists, and screws at ~350 per 100 square feet — so the lumberyard order is right the first time.

Why people use this

Weekend deck builders use it to write one lumberyard order instead of three; estimators use it as a sanity check before quoting. The board-coverage math (5.625" per row) and the 350-screws-per-100-sqft rule are exactly the numbers people estimate by feel and get wrong.

How it works

1. Enter deck length and width in feet.
2. Pick your decking board length and joist spacing (16" standard; 12" for many composites).
3. Read the board count (10% waste included), joist count, and screw quantity.
4. Open the cost section for editable decking, joist, and labor rates.

Common questions

How many deck boards do I need for a 16×12 deck?

Rows across the 12-ft width: ⌈144 ÷ 5.625⌉ = 26 rows, times 16 ft = 416 linear feet. From 16-ft boards with 10% waste that is 29 boards. Shorter boards cost less each but add butt joints — keep joints staggered over joists.

Does this include footings, beams, and railing?

No — those are structural and code-driven. Footing count and depth depend on your frost line and soil, beam spans on lumber species and load, and railing on height. Check your local code and the IRC span tables before digging.

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