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Deck Calculator for Decking Boards, Joists & Fasteners

Calculate deck boards, total linear feet, framing joists, and fastener counts with standard 16-inch on-center spacing.

Quick Answer:To calculate deck boards: divide deck area by the board width in feet, add a 10% waste buffer, and divide by chosen board length (8ft, 10ft, 12ft, 16ft).

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How to Use the Deck Calculator (Decking Boards, Joists & Screws)

1Enter the length and width of the deck in feet.
2Select your decking board length (standard 8, 10, 12, or 16 ft).
3Confirm board width (standard 5.5 inches for nominal 6-inch deck boards).
4Review the total boards, total linear footage, joist count, and screws.

Formula & How It Works

Prescriptive Residential Deck Sizing (AWC DCA 6)

Linear Ft = (L × W) / (5.5 / 12) × 1.10

Deck Area = L × W. Linear Feet = Area / (Board Width in ft) × (1 + Waste). Joists = ⌈(Length in inches) / (Joist Spacing)⌉ + 1. Fasteners = ~3.5 screws per sq ft.

Worked Examples

12x16 Deck with 12ft Boards

Input: 16' L × 12' W, 12ft Boards, 16" Joist Spacing, 10% Waste

Explanation: Area = 192 sq ft. Raw linear ft = 419 ft + 10% waste = 461 linear ft. 461 / 12 = 39 boards.

Result: 39 boards (12ft), ~461 linear ft, 13 joists, ~672 screws

10x10 Small Patio Deck

Input: 10' L × 10' W, 10ft Boards

Explanation: Area = 100 sq ft, requires 240 linear feet of 5.5-inch wide boards.

Result: 24 boards (10ft), 9 joists, ~350 deck screws

16x20 Large Entertaining Deck

Input: 20' L × 16' W, 16ft Boards

Explanation: 320 sq ft area calculated with standard 16-inch on-center joist framing.

Result: 48 boards (16ft), 16 joists, ~1,120 screws

Frequently Asked Questions

What is the actual width of a 6-inch deck board?▼

Standard nominal 5/4x6 decking boards have an actual finished width of 5.5 inches (140 mm).

What is standard deck joist spacing?▼

Standard joist spacing is 16 inches on-center for wood boards, and 12 to 16 inches on-center for composite boards (check manufacturer specifications).

How many screws do I need per square foot?▼

Typically 3.5 screws per square foot (each board is secured with two screws at every joist intersection).

How much gap should be left between deck boards?▼

Wet pressure-treated wood is installed with a tight 1/16-inch gap (it shrinks as it dries); dry composite boards require 1/8 to 3/16-inch spacing.

What waste percentage is recommended?▼

A 10% waste buffer is standard for rectangular decks; use 15% for diagonal or herringbone patterns.

Are calculations private?▼

Yes, all measurements remain completely private inside your browser.

Quick Reference & Conversion Table

Deck Size	Area (sq ft)	Linear Ft (5.5" board)	12ft Boards	16ft Boards
10' × 10'	100	240 ft	20	15
12' × 12'	144	346 ft	29	22
12' × 16'	192	461 ft	39	29
16' × 20'	320	768 ft	64	48

⚠️ Common Pitfalls to Avoid

•Using nominal lumber dimensions (6 inches) instead of actual dimensions (5.5 inches) for 5/4x6 decking.
•Failing to account for board end overhangs and cutting waste around posts and stairs.
•Using standard drywall or interior screws instead of corrosion-resistant exterior composite/deck screws.

💡 Practical Real-World Uses

•Pressure-treated pine, cedar, and redwood patio deck planning.
•Composite (Trex, TimberTech) decking material budgeting.
•Outdoor dock, boardwalk, and porch flooring estimation.

Wood Decking vs Composite Decking

✓Pressure-treated wood is budget-friendly upfront but requires periodic sealing, staining, and splinter maintenance.
✓Composite decking has a higher initial material cost but offers superior rot, splinter, and UV fade resistance with no staining required.

Last reviewed & updated: 2026-11-01

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