Deck Calculator
Your estimate
Deck boards29
Board rows26
- Joists
- 13
- Screws
- 676
- Area
- 192 ft²21.33 yd² · 17.84 m²
- Estimated cost
- $725
Decking boards, joists and screws for a rectangular deck — wood or composite.
Updated 2026-10-20 · Based on: standard lumber and sheet sizes.
How to use the Deck Calculator
- Enter the deck length (the direction the boards run) and the width.
- Enter the board width (5½ in for 5/4 × 6), the gap and the board length you buy.
- Set the joist spacing (16 in on center is standard).
- Read boards, joists and screws.
Formula
Rows of boards = deck width ÷ (board width + gap). Boards per row = deck length ÷ board length (rounded up).
Joists = deck length ÷ spacing + 1. Screws = 2 per board per joist.
Worked example
With the values preset in the calculator above:
- Deck length (along the boards)
- 16 ft
- Deck width
- 12 ft
- Board width
- 5.5 in
- Gap between boards
- 0.1875 in
- Board length
- 16 ft
- Joist spacing
- 16 in
- Extra for waste
- 10 %
- Deck boards
- 29
- Board rows
- 26
- Joists
- 13
- Screws
- 676
- Area
- 192 ft² (21.33 yd²)
Deck joist spacing
- Wood deck boards (5/4 or 2×): 16 in on center; 2×6 boards can span 24 in.
- Composite and PVC boards: usually 16 in, 12 in for diagonal layouts.
- Joist size and span depend on the lumber, load and local code — see IRC table R507.6.
Frequently asked questions
How many deck boards for a 16 × 12 deck?
With 5½ in boards, 3/16 in gaps and 16 ft boards: 29 boards including 10 % waste.
What gap should deck boards have?
About ⅛–¼ in (3–6 mm) for drainage; follow the maker’s spacing for composite boards.
How much does it cost to build a deck?
Roughly $30–$60 per ft² for pressure-treated wood and $50–$100 for composite, built by a contractor in 2026.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.