Deck calculator
Linear feet of decking, board rows, joists and screws for a rectangular deck.
Calculator
Detailed breakdown
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How to use this calculator
Measure
Enter the deck size in feet. Board width defaults to 5.5 inches, the actual width of a nominal 2x6 or 5/4x6 deck board.
Calculate
Once you hit calculate, results update as you type. Change any number to compare options instantly.
Order
Print the estimate and take it to your supplier. Quantities are rounded up so you don't come up short.
Boards run across joists, so count the rows across the width
Decking runs perpendicular to the joists, which means the number of board rows is set by the deck's width and each board spans its length. A 16 by 12 foot deck with 5.5 inch boards and a 1/4 inch gap needs 26 rows: 144 inches of width divided by 5.75 inches of board-plus-gap. Twenty-six rows at 16 feet is 416 linear feet, or 458 linear feet once you add 10 percent for waste.
Use the actual board width, not the nominal one. A nominal 2x6 deck board is 5.5 inches wide, and a 5/4x6 is the same. Estimating on 6 inches undercounts your rows by roughly 8 percent — on this deck that's two rows short.
Underneath, joists at 16 inches on center across a 16 foot length come to 13 joists at 12 feet each — 156 linear feet of framing. With two screws at every board-joist crossing that is 676 deck screws, so buy by the pound and buy more than you think.
This is a material count, not a framing design. The width you entered is the joist span, and span is what sizes the lumber — a 12 foot span at 16 inches on center needs at least a 2x8 in most species, while a 2x6 runs out somewhere under 10 feet. Joist size, beam placement, post footings and how the ledger attaches to the house are all sized by span and load, not by a material count. Use the American Wood Council's DCA 6 prescriptive deck guide or your building department, and expect to need a permit and an inspection: ledger failures are the most common cause of deck collapses.
Check this before you frame: composite decking usually requires 12 inch joist spacing, not 16, and 12 inches or less for a diagonal pattern. Composite is less stiff than wood and sags between widely spaced joists. The manufacturer's span table is the authority, and getting this wrong means re-framing after the joists are already in.
Frequently asked questions
How many deck boards for a 16 by 12 foot deck?
About 26 rows of board, which at 16 feet each is 416 linear feet, or roughly 458 linear feet with 10 percent waste.
How wide is a deck board really?
A nominal 2x6 or 5/4x6 deck board is 5.5 inches wide. Estimating on 6 inches will leave you short by about 8 percent.
What gap should I leave between deck boards?
About a quarter inch for drainage and airflow. Wet pressure-treated lumber shrinks as it dries, so it can be laid tighter and will open up on its own.
What joist spacing does composite decking need?
Usually 12 inches on center rather than 16, and 12 or less for diagonal patterns. Always check the manufacturer's span table before framing.
How many screws for a deck?
Two per board at every joist crossing. A 16 by 12 deck with 26 rows and 13 joists needs about 676 screws.
What size joists do I need?
This calculator does not tell you — and no material calculator can. Joist size depends on the span, the species and grade of lumber, the spacing and the load. The deck width you enter here is the span. Use the American Wood Council's DCA 6 guide or your building department, and get the ledger detail right: ledger attachment is the most common point of failure in deck collapses.
Sources
Formulas and material assumptions on this page follow published industry guidance: