Deck Calculator

Count decking boards, joists, footings and screws for a rectangular deck, with the joist size checked against common span tables.

The Deck Calculator runs entirely in your browser. Your measurements are processed on your device and never uploaded.

Open the Concrete Calculator

Deck Calculator について

A deck is three counting problems stacked on top of each other, and each one is usually out by one. Boards fill the width at board-plus-gap pitch, joists run across the length at their on-centre spacing, and footings sit under every beam line — all three are fencepost counts where the answer is spans plus one, which means one extra board, one extra joist and one extra hole in the ground. This calculator works all three from the deck's dimensions, converts decking into whole boards at the stock length you can actually buy, checks whether the width is within span for common joist sizes, and figures screws at two per board-to-joist crossing, which is the number that surprises people at the till.

機能

Deck Calculator の使い方

  1. Enter the deck length and width in feet
  2. Choose the board width, gap and stock length you plan to buy
  3. Pick the joist spacing — 16 inches on centre is standard
  4. Read the board, joist, footing and screw counts

例

入力

20 × 12 ft deck · 5.5 in boards, 1/8 in gap · 16 ft stock · joists 16 in OC · 10% waste

出力

26 board rows → 58 boards · 16 joists (192 linear ft, try 2x10) · 12 footings · about 832 screws

The 26th row exists because the last gap is not needed — division alone gives 25.

よくあるエラーとトラブルシューティング

よくある質問

How many deck boards do I need for a 20 by 12 foot deck?
With 5.5 inch boards and a 1/8 inch gap you need 26 rows across the 12 foot width. At 16 foot stock that is two boards per row, so 52 before waste and about 58 with a 10% allowance.
What gap should I leave between deck boards?
About 1/8 inch for kiln-dried lumber that will shrink, and 1/4 inch for wet pressure-treated boards that are already at full width. Composite decking follows the maker's spacing, which is usually 3/16 to 1/4 inch for drainage and expansion.
Should joists be 16 or 24 inches on centre?
16 inches is standard and required for most composite decking. 24 inches uses fewer joists but makes the deck feel springy and rules out diagonal boards, which effectively increase the span by about 40%.
How many footings does a deck need?
One under every post, with posts spaced along each beam and a beam line every 8 feet or so of deck width. A 20 by 12 foot deck typically needs three beam lines of four posts, so twelve footings.
How many screws per deck board?
Two at every joist crossing, so a 16 foot board over joists at 16 inch centres takes about 24. Across a whole deck that runs into the hundreds — buy by weight rather than counting boxes.

関連ツール

すべての ArrayKit ツール