Should I use 5/4 or 2x6 deck boards?

Both are 5-1/2 in wide. 5/4 (1 in thick) spans 16 in joists; 2x6 (1-1/2 in) is stiffer and spans 24 in. Check the span rating for composite.

Deck Board Calculator (Boards, Linear Feet and Screws)

Give the deck’s size, the board you are using and the gap you will leave, and this calculator works out the rows of decking, the boards to buy at your chosen length, the total linear feet with waste and the screws or fasteners at two per board per joist. It flags the rip cut on the last row and the butt joints when the deck is longer than the boards. For the framing under the boards use the deck joist span and beam span calculators.

Deck boards calculator

How it works

Rows = deck width × 12 ÷ (board face width + gap), rounded up
Boards per row = deck length ÷ board length, rounded up
Linear feet = rows × deck length, plus waste
Screws = rows × joists × 2, where joists = deck length × 12 ÷ joist spacing + 1

A 5/4×6 or 2×6 board has a 5-1/2 in face; a 2×4 is 3-1/2 in. Composite boards are usually 5-1/2 in with the maker’s specified gap.

Worked example

A 16 × 12 ft deck with 5/4×6 boards running the 16 ft way, 1/8 in gaps, 16 ft boards, joists 16 in on centre:

Deck length (the way the boards run): 16 ft
Deck width (across the boards): 12 ft
Board: 5/4×6 or 2×6 (5-1/2 in face)
Gap between boards: 0.125 in
Board length you will buy: 16 ft
Joist spacing: 16 in on centre
Waste: 5%
Price per linear foot (optional): $0

The calculator gives:

Deck boards to buy: 28 × 16 ft (26 rows, 1 per row, + 5% waste)
Linear feet: 437 ft (416 ft laid)
Screws: 676 (2 per board per joist, 13 joists at 16 in)
Deck area: 192 sq ft (17.8 m²)
Coverage per row: 5.625 in (5.5 in board + 0.125 in gap)

Twenty-six rows of one board each is 416 linear feet; with 5% waste, 28 boards (437 ft). Thirteen joists at two screws each per board is 676 screws, about 7 lb of 2-1/2 in deck screws. The 26 rows cover 146-1/4 in, so the last board is ripped to about 3-3/8 in; widening the gaps to 1/4 in would let 25 full boards fill the width instead.

Notes and limits

Wet pressure-treated boards shrink as they dry; many builders lay them tight and let the gap open. Kiln-dried and composite boards need the gap from the start.
Run boards perpendicular to the joists. Diagonal decking adds about 15% waste and needs blocking.
Butt joints must land on a joist with each end fastened; stagger them across rows.
Composite makers specify gap, joist spacing (often 12 in for diagonal) and fastener type; their instructions override these defaults.
Fascia, stair treads, railing and the framing are not included.

Frequently asked questions

How many deck boards do I need for a 12×16 deck?

With 5-1/2 in boards and 1/8 in gaps, 26 rows of 16 ft boards: 28 boards with 5% waste, about 437 linear feet.

What gap between deck boards?

1/8 in for kiln-dried wood; wet treated lumber is often laid tight. Composite boards usually need 1/4 in, or the gap the maker specifies.

How many screws per deck board?

Two at every joist. A 16 ft board over joists 16 in on centre takes 26 screws.

How many linear feet of decking per square foot?

About 2.13 linear feet of 5-1/2 in board (with 1/8 in gap) per square foot of deck, or 3.3 ft of 2×4.

Should I use 5/4 or 2×6 deck boards?

Both are 5-1/2 in wide. 5/4 (1 in thick) spans 16 in joists; 2×6 (1-1/2 in) is stiffer and spans 24 in. Check the span rating for composite.

Sources

Last reviewed: 26 September 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.