What is the actual width of a 2×6 deck board?

Lumber dimensions are nominal, not actual. A nominal 2×6 board measures approximately 1.5 in. thick by 5.5 in. wide. A nominal 5/4×6 (a common decking board) is actually about 1 in. thick by 5.5 in. wide. Always use the actual face width in this calculator.

How wide should the gap between deck boards be?

A 1/8 in. (0.125 in.) gap is the minimum recommended for drainage and expansion. Most builders use 3/16 in. (0.1875 in.) to 1/4 in. (0.25 in.). For composite decking, check the manufacturer specification — some require larger gaps.

Why does board direction matter?

Boards run perpendicular to the joists. If your joists run the width of the deck, boards run the length, and you calculate how many fit across the width — and vice versa. Choosing the wrong direction wastes material and may require more splices.

How much waste should I add?

Add 10% for straight runs with no obstacles. Add 15% for diagonal patterns, curves, or decks with cutouts. Add up to 20% for very short boards or complex shapes where offcuts cannot be reused.

Does the calculator account for board length?

Yes. Enter the purchase length (e.g., 16 ft) and the calculator determines how many boards of that length cover the run, including any partial boards at the end.

What is linear footage and why does it matter?

Linear footage (LF) is the total length of boards you need end-to-end. Many lumber dealers price decking by the linear foot, so this number translates directly to your material cost estimate.

Deck Board Calculator

Name: Deck Board Calculator
Availability: InStock
Author: Nham Vu

Enter your deck dimensions, board width, gap spacing, and waste factor to get an exact deck board count and coverage estimate.

Deck Parameters

Deck Length (ft)

Deck Width (ft)

Board Run Direction

Boards run perpendicular to the joists.

Actual Board Face Width (inches)

Nominal 2×6 or 5/4×6 = 5.5 in. actual. Check your board.

Gap Between Boards (inches)

Typical: 1/8 in. (0.125) to 1/4 in. (0.25).

Board Purchase Length (ft)

Waste Buffer (%)

10% for straight; 15–20% for diagonal or cutouts.

Fill in your deck details and click Calculate to see your board count.

Summary

Enter your deck dimensions, board width, gap spacing, and waste factor to get an exact deck board count and coverage estimate.

How it works

Enter the deck length and width in feet.
Choose the board run direction — length-wise or width-wise.
Enter the actual face width of each deck board in inches (e.g., 5.5 in. for a nominal 2×6).
Set the gap between boards in inches (typically 0.125–0.25 in.).
Enter the length of boards you plan to purchase (e.g., 8, 12, or 16 ft).
Add a waste percentage (10% is standard for straight runs; 15% for diagonal or complex layouts).
The calculator returns total board count, linear footage, and a full breakdown.

Use cases

Estimating materials for a new backyard deck build.
Replacing worn or damaged boards on an existing deck.
Comparing costs between different board widths or lengths.
Planning material quantities before visiting the lumber yard.
Calculating waste-adjusted quantities for diagonal decking patterns.
Budgeting a composite decking project with fixed board dimensions.
Estimating decking for a dock, boardwalk, or porch floor.
Cross-checking a contractor quote for material quantities.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu