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Deck Board & Lumber Quantity Calculator

Compute deck boards, total linear feet, joists, and fastener counts for decks.

Quick Answer:Divide deck surface area by effective board width (including spacing gaps) to determine total linear feet, then divide by stock board length.

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How to Use the Deck Board Calculator: Lumber Count & Fastener Sizing

1Input deck length and deck width in feet.
2Select your stock deck board length (12ft, 16ft, or 20ft lumber).
3Set your board width (5.5 inches for standard 5/4x6 decking) and spacing gap.
4Review your calculated board count, total linear feet with waste buffer, joists, and screws.

Formula & How It Works

Deck Material Equations

Linear Feet = Area / (Board Width + Gap in ft) × (1 + Waste%) | Boards = Linear Feet / Board Length

Calculates decking boards, framing joists, and fasteners based on deck geometry.

Worked Examples

16' × 12' Backyard Deck with 16-ft Boards

Input: Length: 16 ft, Width: 12 ft, Stock: 16 ft boards, 10% Waste

Explanation: Covering 192 sq ft with 5.5" boards requires 28 full 16-foot deck boards with 10% cutting scrap buffer included.

Result: 28 Boards (16ft) | 442 Linear Feet | 13 Joists | ~670 Screws

Frequently Asked Questions

What is the actual width of a 5/4 x 6 deck board?▼

Nominal 5/4 x 6 decking boards actually measure 1 inch thick by 5.5 inches wide.

What gap should I leave between deck boards?▼

Leave a 1/8" to 3/16" gap between dry or composite boards for drainage; wet pressure-treated wood can often be installed tighter as it will shrink as it dries.

How many screws are needed per deck board at each joist?▼

Install two screws per board at every joist intersection (e.g. for a 5.5" board over a 1.5" joist).

Should deck boards be laid bark side up or bark side down?▼

Most carpenters recommend bark side up (annual growth rings arching downward) to minimize cupping and water pooling as the wood seasons.

Quick Reference & Conversion Table

Deck Size	Square Footage	16-ft Boards Needed	Linear Feet (10% Waste)
10 ft × 12 ft	120 sq ft	18 boards	276 lin ft
12 ft × 16 ft	192 sq ft	28 boards	442 lin ft
16 ft × 20 ft	320 sq ft	46 boards	736 lin ft
20 ft × 24 ft	480 sq ft	69 boards	1,104 lin ft

⚠️ Common Pitfalls to Avoid

•Forgetting to include a 1/8" to 3/16" expansion gap between wet pressure-treated or composite decking boards.
•Using 16" on-center joist spacing for diagonal 45-degree decking patterns (diagonal layouts require 12" on-center joists).

💡 Practical Real-World Uses

•Ordering lumber packages from building supply yards for DIY patio decks.
•Comparing material costs between pressure-treated pine, cedar, and Trex composite decking.

Last reviewed & updated: 2026-11-11

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