DeckTally

Deck Material Calculator

Enter your deck size to see how many boards, joists and screws to buy, with the working shown for every number.

Units

Boards run along this side.

Actual width, not nominal. A nominal 6-inch board is 5.5 in (139.7 mm).

Center to center.

0 to 25%.

Optional. Any currency.

Your materials

Boards to buy
29 boards
16 ft long
Joists
13 joists
12 ft long
Deck screws
676 screws
Board cost
—

How it adds up

  1. Deck area 192 sq ft

    16 ft × 12 ft = 192 sq ft

  2. Rows of boards 26 rows

    Each row: 5.5 in board + 0.25 in gap = 5.75 in 144 in of deck width ÷ 5.75 in = 25.04, rounded up to 26

  3. Decking needed 416 linear ft

    26 rows × 16 ft = 416 ft

  4. Boards to buy 29 boards

    416 ft × 1.10 (10% waste) = 457.6 ft 457.6 ft ÷ 16 ft per board = 28.6, rounded up to 29

  5. Joists 13 joists

    192 in of deck length ÷ 16 in spacing = 12 12 + 1 for the far end = 13

  6. Deck screws 676 screws

    26 rows × 13 joists × 2 screws per crossing = 676

  7. Board cost —

    Enter a price per board to estimate the cost.

Estimates only. Results come from the formulas listed below and use no outside data. Check local building codes and your supplier before buying.

Your deck

Plan of a deck 16 ft long and 12 ft wide, with 26 rows of boards and 13 joists. Length 16 ft Width 12 ft
  • 26 rows of boards, running along the length
  • 13 joists, 16 in apart

How to use the calculator

  1. Measure the deck. Enter the side the boards run along as the length, and the other side as the width.
  2. Enter the actual width of your deck boards and the gap you will leave between them.
  3. Pick the board length you will buy and how far apart your joists are, measured center to center.
  4. Set a waste allowance. The default is 10%.
  5. Add a price per board if you want a cost estimate.

The results update as you type, and each one shows the sum behind it. Switch to metric at the top of the form if you measure in meters and millimeters. The page address updates too, so you can bookmark or share your numbers.

How the numbers are calculated

Rows, boards and joists are always rounded up, because a partial row or a partial board still has to be bought. The About page explains how every DeckTally calculator works.

Worked example

A 16 × 12 ft deck with 5.5-inch boards, a 0.25-inch gap, 16 ft boards, joists at 16 inches and 10% waste:

So you would buy 29 boards, 13 joists and 676 screws.

Common board sizes

Deck boards are sold by a nominal size, but the actual width is smaller. Enter the actual width in the calculator.

Nominal widthActual width
6 in5.5 in

What this calculator leaves out

FAQ

How much decking do I need?

A 16 × 12 ft deck with 5.5-inch boards and a 0.25-inch gap needs 29 boards 16 ft long, including 10% waste. To work it out, count the rows of boards across the deck (26 here), multiply by the deck length to get linear feet (416), add waste, and divide by the length of board you will buy. Enter your own sizes in the calculator above to get the count for your deck.

How many deck boards per square foot?

With 5.5-inch boards and a 0.25-inch gap, each row covers 5.75 inches, so you need about 2.09 linear feet of board per square foot of deck. The number of boards depends on their length: the 192 sq ft worked example needs 29 boards 16 ft long including 10% waste, about 0.15 boards per square foot.

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

A 12 × 12 ft deck with 5.5-inch boards and a 0.25-inch gap needs 26 rows of boards, or 312 linear feet. With 10% waste that is 29 boards 12 ft long, or 22 boards 16 ft long. With joists at 16 inches it also needs 10 joists and 520 screws.

How far apart should deck joists be?

Closer spacing means more joists: a 16 × 12 ft deck needs 17 joists at 12 inches, 13 at 16 inches and 9 at 24 inches. Joist spacing is measured from the center of one joist to the center of the next, and this calculator lets you choose 12, 16 or 24 inches. This calculator does not set a safe spacing: that depends on your decking and local building code, so check the board maker's instructions and your building department before you choose.

How much waste should I allow for decking?

This calculator adds 10% by default and lets you set anything from 0% to 25%. Waste covers offcuts, damaged boards and cutting mistakes. On the 16 × 12 ft example, 10% waste raises the order from 26 boards to 29.

How many screws do I need for a deck?

A 16 × 12 ft deck needs 676 screws at 2 per board-and-joist crossing: it has 26 rows and 13 joists, and 26 × 13 × 2 = 676, about 3.5 per square foot. To count yours, multiply the rows of boards by the number of joists, then by 2. With joists at 24 inches the same deck has 9 joists and needs 468 screws.

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