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Deck calculator: boards, joists and screws for a deck

The short answer

Divide the deck’s width in inches by the board’s width plus the gap to get rows, multiply by the length, add waste, then divide by the board length you’ll buy. A 16 by 12 foot deck with 5.5 inch boards and a 1/8 inch gap is 26 rows, or 458 feet of board with 10% waste. That’s 29 boards of 16 feet.

Enter the deck and the boards you’re using. You’ll get the boards to order, the joists under them and the screws, plus a price to quote if it’s a customer’s deck.

Checked November 5, 2026. How we make these tools

Decking you need

29 boards

26 rows across 192 square feet, or 458 feet of board with waste.

Joists, before rim joists: 13
Joist length: 12 ft
Face screws, 2 at each joist: 676

Price for this job

29 at $28.00 per deck board: $812.00
13 at $22.00 per joist: $286.00
Labor: $0.00
Markup on materials: $219.60
Materials plus markup: $1,317.60

Add your labor hours to get a price to quote.

How it works

Rows = width (in) ÷ (board width + gap), rounded up.
Feet of board = rows × deck length, plus waste.
Boards = feet of board ÷ the board length you buy, rounded up.
Joists = length (in) ÷ joist spacing, rounded up, plus 1.
Face screws = rows × joists × 2. Hidden fasteners go by the maker’s own count.

Boards for common decks: 5.5 inch boards, 1/8 inch gap, 10% waste, 16 foot lengths
Deck	Square feet	Rows	Boards	Joists at 16 inches
10 × 10 ft	100	22	16	9
12 × 12 ft	144	26	22	10
16 × 12 ft	192	26	29	13
20 × 12 ft	240	26	36	16
24 × 16 ft	384	35	58	19

What this doesn’t count

Beams, posts, footings, ledger, railings and stairs depend on the deck’s height, span and your local code, so they’re not here. Many places require a permit for a deck, and the code sets joist and beam sizes, so check with your building department before you quote. Use the concrete calculator for round footings.

Quoting it

Boards that don’t divide evenly into the deck’s length leave offcuts, so it often pays to buy a length that does. A 16 foot deck uses 16 foot boards with little waste, while a 14 foot deck cut from 16s wastes 2 feet on every row. Put demolition of an old deck and haul-away on an estimate as their own lines.

Common questions

How many deck boards do I need?

Work out the rows from the deck’s width, then the feet of board from its length. A 16 by 12 foot deck takes 29 boards of 16 feet with 5.5 inch boards, a 1/8 inch gap and 10% waste.

How many deck boards for a 12 by 12 deck?

With 5.5 inch boards and a 1/8 inch gap, it’s 26 rows of 12 feet, plus 10% waste. That comes to 29 boards of 12 feet.

How much extra decking should I buy?

This calculator starts at 10%. Diagonal boards, picture frame borders and lots of corners take more, so raise it for those.

How far apart should deck joists be?

The calculator starts at 16 inches, but your local code and your decking maker’s guide decide it. Diagonal boards and some composite boards can need closer spacing, so check before you order.

How do I price a deck job?

Enter what you pay for boards and joists, add framing lumber and hardware under other costs, then your labor hours and rate. Divide the total by the square feet to see your price per square foot.

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