Decking Calculator

Frequently Asked Questions

How many 2x6 boards do I need for a 12x16 deck?

With 0.25 in gaps and 10% waste: 12 ft (144 in) divided by 5.75 in = 26 boards, each 16 ft long. Add 10% waste = 29 boards total.

How much waste factor should I use for decking?

Use 10% for simple rectangular decks. Add 15% for diagonal installs or decks with lots of angles and notches.

What is the difference between 2x6 and 5/4x6 deck boards?

A 2x6 is 1.5 in thick (stronger, better for wider joist spacing), while 5/4x6 is 1 in thick with rounded edges. Both are 5.25-5.5 in wide when dressed.

How do I calculate board-feet for decking?

Board-feet always use nominal dimensions: BF = nominal thickness (in) x nominal width (in) x length (ft) / 12. A 2x6 at 16 ft is 2 x 6 x 16 / 12 = 16 board-feet, or exactly 1 BF per linear foot.

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How This Calculator Works

The calculator divides the deck width (converted to inches) by the combined board and gap width, then rounds up to the nearest whole board. Total linear feet multiplies that board count by the deck length and adds the waste factor. Board-feet use the NOMINAL dimensions of the lumber, which is how board-feet are defined in the trade: BF per linear foot = nominal thickness (in) x nominal width (in) / 12. A 2x6 is exactly 1.0 BF per linear foot, a 2x4 is 0.667, and a 5/4x6 deck board is 1.25 x 6 / 12 = 0.625.

Formula: boards = ceil(deck_width_in / (board_width_in + gap_in)). Linear feet = boards x deck_length x (1 + waste/100). Board-feet = nominal_t x nominal_w x linear_feet / 12.

Common Deck Board Sizes

Actual dimensions differ from nominal sizes due to surfacing:

2x6 nominal = 1.5 in x 5.5 in actual - the most popular residential deck board

2x4 nominal = 1.5 in x 3.5 in actual - used for smaller decks or aesthetic patterns

5/4x6 (deck board) = 1 in x 5.25 in actual - designed specifically for deck surfaces

Composite decking: widths vary by brand, typically 5.25-5.5 in

Board Spacing Guidelines

A 0.25 in (1/4 in) gap between boards is standard for new pressure-treated lumber. As the wood dries it will shrink slightly and the gap may widen to 3/8 in. For composite decking follow the manufacturer's specification, often 3/16 in. Gaps allow water drainage and air circulation, preventing rot and warping. On angled installs (diagonal pattern) the gaps appear narrower when viewed straight on.

FAQ

How many deck boards for a 12x16 ft deck?

Using 2x6 boards (5.5 in) with 0.25 in gaps: deck width of 12 ft = 144 in. Boards = ceil(144 / 5.75) = ceil(25.04) = 26 boards, each 16 ft long. With 10% waste: about 29 boards or 464 linear feet.

What gap should I leave between deck boards?

1/4 in (6mm) for new pressure-treated lumber; 3/16 in for composite decking per most manufacturer specs. Green lumber shrinks as it dries so a 1/4 in gap is fine even though it may look wide at first.

Should I use 2x4 or 2x6 deck boards?

2x6 boards are the standard choice. They span farther between joists (up to 24 in on-center for light use), feel more solid underfoot, and require fewer boards. 2x4 boards work well for decorative patterns or light-duty small decks but need joists no more than 16 in apart.

What lumber species is best for decking?

Pressure-treated Southern yellow pine is the most affordable option. Cedar and redwood resist decay naturally and are beautiful but cost more. Tropical hardwoods like IPE last 30-50 years but require carbide tools and pre-drilling. Composite decking avoids rot and splinters but is more expensive upfront.

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