Skip to the calculator
Rule Calculator

Deck Board Calculator

With deck length 16 ft, deck width 12 ft, board width 5.5 inch, gap between boards 0.1875 inch and 2 more fields, deck board comes to 26 boards — boards to order. It is reached in 6 steps, the last of which is ceil(416 / 16), and each one is printed on the page with its numbers filled in. The formula is the one published by American Wood Council DCA 6, not an approximation fitted to it.

Decking boards, joists and fasteners for a rectangular deck, accounting for the gap between boards.

Formula and sources checked · How we check

Deck length 16 ft, Deck width 12 ft, Board width 5.5 inch, Gap between boards 0.188 inch

26 boards

Boards to order for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.

It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.

deck lengthdeck widthgap
What to measure
Boards to order
26 boards
Rows of decking
ceil(12 * 12 / (5.5 + 0.1875))26 rows
Linear feet of decking
26 * 16416 ft
Boards to order
ceil(416 / 16)26 boards
Joists
ceil(16 * 12 / 16) + 113 joists
Screws (two per joist crossing)
26 * 13 * 2676 screws
Deck area
16 * 12192 sq ft

Several at once

A job is rarely one of anything. Work out the first, add it, change the figures and add the next — the list keeps what each line was, and totals them.

Ask about this in the chat

Worked example

A 16 × 12 deck takes 26 rows at 5.5 in plus a 3/16 in gap — 416 linear feet, so 26 sixteen-foot boards with no butt joints at all. Ordering 12 ft boards instead would put a seam in every row.

How to work it out yourself

  1. 1.Measure the deck. Length runs parallel to the boards; width is the direction they span.
  2. 2.Divide the width in inches by the board width plus the gap, and round up. That is the number of rows.
  3. 3.Multiply rows by deck length for total linear feet, then divide by the length of board you can buy.
  4. 4.Count joists as deck length in inches divided by joist spacing, plus one for the far end.
  5. 5.Allow two screws per board at every joist crossing.

The formula

  1. Rows of deckingceil(12 * 12 / (5.5 + 0.1875))
  2. Linear feet of decking26 * 16
  3. Boards to orderceil(416 / 16)
  4. Joistsceil(16 * 12 / 16) + 1
  5. Screws (two per joist crossing)26 * 13 * 2
  6. Deck area16 * 12

Source: American Wood Council DCA 6 — prescriptive residential deck construction, International Residential Code R507 — decks

Questions people actually ask

Why does the gap matter so much?
It is what stops the deck cupping and holding water. Wet-treated lumber arrives swollen and shrinks, so it gets a tight 1/8 in gap; kiln-dried and composite boards do not shrink and need the full 3/16 in built in.
Can I space joists at 24 inches?
Only for perpendicular decking rated for it. Diagonal layouts and most composites require 16 in, and composites often drop to 12 in for diagonal runs — check the board manufacturer before the framing goes down.
Should I buy boards longer than the deck?
Buy the exact length if it exists. A 16 ft board on a 16 ft deck has no butt joint, and every butt joint needs doubled blocking underneath and becomes a water trap later.

Related

Part of a job

Read first

  • What a Deck Costs to Build — Decking, framing and fasteners priced out, and why the board decides the total: the framing under it barely changes between a cheap deck and a costly one.

Put this calculator on your site

Free, no attribution required beyond the link.

<iframe src="https://rulecalculators.com/embed/deck-boards" width="100%" height="420" style="border:1px solid #e7e4de;border-radius:12px" title="Deck Board Calculator"></iframe>
Did this answer your question?