Material estimator

Decking Calculator

Estimate deck boards, board courses, linear feet, waste, and board cost for a simple rectangular deck surface.

How This Calculator Works

Decking is ordered by board count and length, not just square footage. This calculator estimates board courses across the deck width and total linear feet to buy.

Formula

Board courses = deck width / (board face width + gap). Linear feet = courses x deck length + picture-frame length. Boards = linear feet / board length, rounded up.

Assumptions

The default board face is 5.5 inches with a 1/8 inch gap and 12 ft boards. Picture-frame borders, stairs, diagonal decking, and seam layouts can change the order.

Practical Examples

A 16 ft by 12 ft deck using 5.5 inch boards, 1/8 inch gaps, 12 ft board lengths, and 10% waste needs about 39 deck boards.
A 12 ft by 12 ft deck with 5.5 inch boards, 1/8 inch gaps, 12 ft boards, and 10% waste needs about 29 boards.
A 20 ft by 14 ft deck with 16 ft boards and 10% waste needs about 54 boards before stairs, railing, and picture-frame trim.
Adding 56 linear feet of picture-frame border to a 16 ft by 12 ft deck with 10% waste increases the estimate from about 39 to about 44 twelve-foot boards.

Before You Buy

Buying Guidance

Use this for surface deck boards only. Framing, posts, beams, joists, stairs, railing, blocking, and fasteners need separate estimates.
Confirm actual board face width. Nominal board names often differ from the installed face width.
Longer boards reduce butt joints but can cost more, be harder to transport, and require better layout planning.

Waste Rules

Use 10% waste for simple perpendicular decking and more for diagonal boards, picture frames, breaker boards, or complex perimeters.
Add picture-frame or border boards as linear feet so they are not lost inside the field-board estimate.

Common Mistakes

Do not use square footage alone for decking because board width, gaps, and board length control the actual count.
Do not ignore code and structural design. This page estimates surface boards, not whether the deck is safe to build.

Plan the Rest of the Job

Common Questions

Does this estimate framing?

No. This estimates deck surface boards only, not joists, beams, posts, footings, railings, stairs, or fasteners.

How much decking waste should I add?

Use 10% for simple perpendicular boards and more for diagonal layouts, borders, seams, or complex cuts.

Why does board gap matter?

The gap changes how many board courses fit across the deck width.