What is the actual size of a 5/4×6 deck board?

Decking Calculator

Calculate decking boards, screws, and joists for your deck project. Supports various board widths.

Deck Dimensions (Feet)

Deck Length (along house)

Deck Width (out from house)

Board Specifications

Width (in)5.5 in std

Length (ft)12/16/20 ft

Gap (in)0.25 in std

Waste Allowance (%)

Decking Materials Estimate

SPEC_VERIFIED

Deck Boards Needed (16 ft planks)

561boards

Detailed Material Breakdown

Total Deck Surface Area: 320 sq ft
Estimated Framing Joists (16" OC): 16joists
Estimated Fasteners / Screws: 640screws

ℹThis estimator provides approximate board, joist, and fastener counts. Joist sizing (e.g. 2x8 vs 2x10) and post footing depth depend on local building codes and frost depth requirements.

Calculation Formula & Assumptions

Calculates surface decking boards, joists, and fastener counts for attached or freestanding residential decks.

Boards = ⌈(Deck Area ÷ Board Area) × (1 + Waste %)⌉

Step-by-step breakdown:

Deck Area = Length × Width
Effective board width = Board Width + Gap Width
Board Rows = Deck Width ÷ Effective Board Width
Linear Feet = Board Rows × Deck Length × (1 + Waste %)
Joists = ⌈Deck Length in inches ÷ Joist Spacing in inches⌉ + 1
Fasteners = Approx. 3.5 screws per square foot of deck.

Note: Composite decking typically requires 12" on-center joist spacing for diagonal layouts or 16" for straight layouts.

Worked Calculation Example

Backyard Deck (16×20 ft)

Building a 16 ft by 20 ft deck with 16-foot 5/4×6 composite boards spaced 1/4" apart.

Deck Dimensions:16 ft wide × 20 ft long (320 sq ft)

Board Sizing:5.5" actual width × 16 ft long

Gap:0.25 inches

Waste Factor:10%

Calculation Steps:

Deck Area = 16 × 20 = 320 sq ft
Effective board width = 5.5 + 0.25 = 5.75 in (0.479 ft)
Board rows = 20 ft ÷ 0.479 ft = 41.7 => 42 rows of 16-foot boards
With 10% waste: 42 × 1.10 = 46.2 => 47 boards (16 ft length)
Screws required = 320 sq ft × 3.5 = 1,120 deck screws

Order 47 sixteen-foot deck boards, 16 framing joists, and 1,200 deck screws.

How to Use This Calculator

Enter deck length and width.
Select nominal board size (standard 5/4×6 boards have an actual width of 5.5 inches).
Select board length (8, 12, 16, or 20 feet).
Set board expansion gap (typically 3/16" or 1/4").