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Deck Calculator

Decking a 16 by 12 ft deck with 5.5-inch boards 16 feet long takes 29 boards, or 464 linear feet of lumber, with 10 percent waste included. Looking for shower pan mortar instead? This page is about lumber decks; the deck mud calculator covers the sand and cement mix under a tile shower floor.

Deck specs

Your board count

Deck area--
Deck boards needed--
Linear feet--

Estimates only.

Chris Terry
Built and maintained by Chris Terry, Owner and Editor
Updated July 18, 2026
LENGTH (FT) WIDTH (FT)
How the calculator reads your measurements

The math behind the board count

Each board covers a strip equal to its width (converted to feet) times its length. Divide total deck area by coverage per board, then multiply by the waste factor and round up. Multiply board count by board length to get total linear feet for your lumber order.

Board coverage and joist spacing here track Decks.com's framing guide and Inch Calculator's lumber math, both cited below.

Board count comes down to deck area divided by what one board covers, plus about 10% for waste. A 5/4x6 board is 5.5 inches wide, which is roughly 0.46 ft, so a 16 ft board covers about 7.3 ft².

Formula: Coverage per board = (Board width in / 12) x Board length ft. Boards = ceil(Deck area x (1 + Waste% / 100) / Coverage per board). Linear feet = Boards x Board length.

A worked example

Take a 16 by 12 deck. That is 192 ft². A 16 ft board of 5.5 inch decking covers about 7.33 ft², so 192 divided by 7.33 is just under 27 boards. Add 10% waste and round up and you land on about 29 boards. At 16 ft each that is roughly 464 linear feet, which is the number you actually hand to the lumber yard. If you run boards diagonally for looks, push waste toward 15% because the angled cuts leave longer offcuts.

How to measure a deck

Multiply length by width for the surface area. Decks are rarely a clean rectangle, so break wraparounds, bump-outs and stair landings into separate rectangles and add them. The framing underneath is a different question from the boards on top: joists sit 16 inches on center for standard wood decking, and many composite boards call for 12 inches on center so the surface does not feel springy. Always check the decking manufacturer span chart before you set joist spacing.

Board coverage and spacing

DetailValue
5/4x6 board width5.5 in (about 0.46 ft)
Coverage, 16 ft boardabout 7.3 ft²
Joist spacing, wood decking16 in on center
Joist spacing, compositeoften 12 in on center
Gap between boards1/8 to 1/4 in
Waste to add10% straight, 15% diagonal

Tips from the field

Order full lengths that match your run where you can. A 16 ft deck framed for 16 ft boards has no butt joints to stagger, which looks cleaner and wastes less. Leave a 1/8 to 1/4 inch gap between boards for drainage and seasonal movement; that gap slightly trims coverage, so the waste factor earns its keep. Buy a few extra boards from the same lot for repairs later, since wood tone and composite color both drift between production runs.

Sources: Decks.com joist spacing guide (16 in OC standard), Inch Calculator for lumber math.

Round out the build

Good to know

Deck board questions

How many deck boards do I need for a 16x12 deck?

A 16 x 12 foot deck is 192 square feet. Using standard 5/4 x 6 decking (5.5 inches wide, 16 feet long) with 10% waste, you need about 27 boards. The calculator above gives you the exact count for your board dimensions.

How do I calculate linear feet of decking?

Multiply the number of boards by the board length. For example, 27 boards at 16 feet each equals 432 linear feet. This is what you order at the lumber yard.

What is the standard deck board spacing?

Most contractors leave a 1/8 to 1/4 inch gap between boards for drainage and expansion. This slightly reduces coverage per board, so add an extra 2 to 3 percent on top of your normal waste factor.

How much does it cost to build a deck per square foot?

Pressure-treated lumber decks typically run $15 to $35 per square foot installed. Composite decking runs $30 to $60 per square foot. Material costs alone are roughly $5 to $15 per square foot depending on species and grade.

What joist spacing should I use?

16 inches on center is standard for wood decking. Composite boards often call for 12 inches on center, so check the manufacturer span chart before framing.

How much waste should I add?

About 10% for boards run straight across, and closer to 15% for diagonal or herringbone patterns where angled cuts leave longer offcuts.

How many boards for a 12 by 12 deck?

That is 144 ft². With 16 ft, 5.5 inch boards and 10% waste you need about 22 boards, or roughly 352 linear feet.

Do I need to subtract the gap between boards?

The 1/8 to 1/4 inch drainage gap slightly reduces coverage per board. The standard waste factor usually covers it, but on a large deck add an extra 2 to 3 percent.