Decking & Lumber Estimator

Deck Board Calculator

Calculate exact deck boards, total linear feet, board feet, screws, and material costs for wood and composite decking.

Deck Dimensions & Layout

Enter the overall dimensions of your deck platform

Deck Length (feet) — Along the boards Direction decking boards will run

Deck Width (feet) — Across the boards Perpendicular to board direction

Deck Board Size (Nominal & Actual)

Purchased Board Length

Gap Between Boards

Waste & Trimming Allowance

Joist Spacing (On-Center)

Material & Cost Estimator

Select typical material pricing or enter your local lumber yard quote

Price per Board ($)

Box of Deck Screws (~350 pcs / $35)

How to Calculate Deck Boards: Math, Formulas & Pro Rules

Accurately estimating deck boards prevents costly job delays and ensures you do not overspend on expensive premium decking materials like composite (Fiberon, Trex) or hardwoods (Cedar, Redwood, Ipe).

1. Number of Board Rows Formula

Deck width is divided by the actual width of one board plus the drainage gap spacing:

Rows = (Deck Width in Feet × 12) ÷ (Actual Board Width in. + Gap in.)

2. Total Linear Footage & Board Count

Multiply total rows by length, factor in waste (10%), and divide by your stock board length:

Total LF = Rows × Deck Length (ft) × (1 + Waste Factor)
Board Count = Total LF ÷ Purchased Board Length

Deck Board Material Comparison

Deck Material	Average Cost	Recommended Gap	Joist Spacing	Maintenance Level
Pressure-Treated Pine (PT)	$1.50 – $2.50 / LF	1/8" (or tight if wet)	16" on-center	Annual power washing & staining
Western Red Cedar	$2.75 – $4.25 / LF	3/16" – 1/4"	16" on-center	Seal every 1–2 years
Fiberon / Trex Composite	$3.80 – $6.50 / LF	3/16" (Thermal expansion)	16" (Perp.) / 12" (Diag.)	Soap and water cleaning only
Ipe / Brazilian Hardwood	$5.50 – $9.00 / LF	1/4" (Air circulation)	16" on-center	UV hardwood oil finishing

Frequently Asked Questions

How do I calculate how many deck boards I need?

Convert your deck width into inches, divide by the effective board width (actual board width + gap spacing) to get the number of board rows. Multiply rows by deck length to get total linear feet, add your waste factor (typically 10%), and divide by your chosen board length (e.g., 12 ft or 16 ft).

What is the difference between nominal and actual deck board size?

A standard 5/4×6 deck board has an actual milled size of 1 inch thick by 5-1/2 inches wide. A 2×6 deck board measures 1-1/2 inches thick by 5-1/2 inches wide. Always use actual dimensions when calculating row coverage and gap spacing.

How much gap should I leave between deck boards?

For wet, green, or pressure-treated lumber right from the yard, leave an 1/8-inch gap (or butt them tight if dripping wet, as they will shrink as they dry). For kiln-dried lumber or composite decking (such as Fiberon or Trex), leave 3/16 to 1/4 inch to allow for water drainage and thermal expansion.

What joist spacing is required for composite decking vs wood?

Standard wood decking boards (5/4x6 or 2x6) run perpendicular across joists spaced at 16 inches on-center (OC). Composite decking (Fiberon, Trex) is more flexible and typically requires 16-inch OC for perpendicular runs and 12-inch OC if boards are installed diagonally (at 45 degrees).

How many screws or fasteners do I need for a deck?

Plan for approximately 350 deck screws per 100 square feet of decking. Standard practice requires two fasteners at every joist intersection for 5.5-inch boards (or hidden clip systems for grooved composite boards).

Specialized Calculators

Choose from our collection of specialized board foot calculators tailored for specific materials and applications

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