BYTETOOLS

Deck Calculator

Work out decking boards, joists, beams, posts, railing and screws from your deck size, board width and joist spacing, with waste, board feet and cost.

192.0
Deck area (sq ft)
17.84
Deck area (m²)
26
Board rows
29
Decking boards to buy
13
Joists
156.0
Joist material (ft)
32.0
Beam material (ft)
3
Posts & footings
40.0
Railing (ft)
88
Balusters
8
Railing posts
676
Deck screws (2 per crossing)
212.7
Decking board feet
0.502
Decking volume (m³)
$1,876.00
Estimated material cost

Board rows = deck width ÷ (board face width + gap); boards = rows × boards per row, plus the waste allowance. Joists = (deck length ÷ on-centre spacing) + 1, each spanning the deck width. Fasteners assume two screws at every board-and-joist crossing. Board feet are worked out from the actual dimensions you entered — lumber is usually priced on the larger nominal size. Joist and beam spans must be checked against your local code span tables, and footing depth against the frost line. Estimates only, not a structural design.

What is the Deck Calculator?

The ByteTools Deck Calculator turns a deck size into a materials list. Enter the length and width, pick a decking board, set the gap between boards and the joist spacing, and it returns the number of boards to buy, how many joists and beams the frame needs, the posts and footings under it, and the railing and fastener counts.

  • Board count from area ÷ (board width + gap) × board length, with a waste allowance
  • Joists, beam plies, posts and footings from your own spans and spacing
  • Railing length, baluster count and railing posts for two, three or four sides
  • Deck screws at two per board-and-joist crossing
  • Board feet and timber volume alongside an itemised cost estimate
  • Imperial and metric input, all running in your browser with nothing uploaded

How to use the Deck Calculator

  1. 1

    Choose imperial or metric and enter the deck length and width — the length is the direction the boards run.

  2. 2

    Pick a decking board size, then fine-tune the face width, thickness, gap and the board length your supplier sells.

  3. 3

    Set the joist spacing, the number of beam rows and plies, and how far apart the posts sit along each beam.

  4. 4

    Choose how many sides get railing and set the baluster spacing.

  5. 5

    Enter prices per board, per foot of framing and per foot of railing, then read the boards, joists, posts, screws and total cost.

About the Deck Calculator

The ByteTools Deck Calculator turns a deck size into a materials list. Enter the length and width, pick a decking board, set the gap between boards and the joist spacing, and it returns the number of boards to buy, how many joists and beams the frame needs, the posts and footings under it, and the railing and fastener counts.

It is built for homeowners pricing a weekend build and for carpenters checking an order before it goes in. Everything is editable — board face width, board length, gap, on-centre spacing, post spacing, baluster pitch, waste allowance and unit prices — so you can model composite decking as easily as pressure-treated pine, in feet or metres.

All the arithmetic runs locally in your browser: nothing you type is uploaded and no measurements leave your device. Joist and beam spans, footing depth and railing height are code matters, so treat this as a shopping estimate and check the numbers against your local span tables before you cut anything.

Frequently asked questions

How many deck boards do I need for a 12x16 deck?

A 12 by 16 ft deck is 192 sq ft. With 5.5 in boards and a 1/8 in gap each board row covers 5.625 in, so you need 26 rows of 16 ft boards — about 29 boards once a 10% waste allowance is added. Enter your own board width and length above for an exact count.

How many joists do I need for a deck?

Joists = (deck length ÷ on-centre spacing) + 1. A 16 ft long deck at 16 in centres needs 13 joists, each spanning the deck width. Drop to 12 in centres if you are laying the boards diagonally, because the diagonal increases the unsupported span between bearing points.

What gap should I leave between deck boards?

About 1/8 in (3 mm) for kiln-dried or composite boards, and close to nothing for wet pressure-treated lumber that will shrink as it dries. The gap matters for drainage and airflow, and this calculator folds it straight into the board count as part of the row pitch.

How many screws do I need for a deck?

Two screws at every point a board crosses a joist. This calculator multiplies the number of board rows by the number of joists and doubles it, which for a typical 12 by 16 ft deck comes to a few hundred — so buy by the box, not the handful.

How much waste should I allow for decking?

Ten per cent is the usual allowance and covers cuts, crooked boards and the odd split. Push it to 15% for a diagonal or herringbone pattern, or for a deck with lots of angles, picture framing or stair treads cut from the same stock.

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