Deck Calculator
A deck calculator works out the materials for a deck from its dimensions: the number of decking boards (from the deck area and board width), the joists (from the span and spacing), and the fasteners. Enter your deck length, width, board size and joist spacing below to get the full materials list and an estimated cost.
Enter deck dimensions to see the materials.
Estimate only. Confirm against your local building code: stairs, framing, rebar, roofing and retaining walls are structural and code-dependent. This site does not provide engineering judgment.
How Do You Calculate Decking Boards?
To calculate decking boards, find the deck area (length times width), then divide by the coverage of one board (board width times length), and add 10 percent waste for cuts and the perimeter. A 12 by 16 foot deck is 192 square feet; with 5.5 inch by 16 foot boards (about 7.3 square feet each) that is about 27 boards, or 30 with waste. The calculator also counts joists and fasteners.
How Many Joists Does a Deck Need?
Deck joists are spaced 12 or 16 inches on center, with 16 inches standard for most residential decking. The joist count is the deck width divided by the spacing, plus one. A 12 foot wide deck at 16 inch spacing needs about 10 joists. Composite decking and diagonal layouts often require 12 inch spacing, which raises the count. The calculator adjusts the joist count to your chosen spacing.
What Fasteners Does a Deck Need?
Decking is fixed with screws or hidden clips at every joist crossing, so the fastener count scales with boards times joists. As a rule of thumb, plan on about 350 screws per 100 square feet of deck with 16 inch joist spacing. A 192 square foot deck needs roughly 670 screws. The calculator estimates fasteners from the board and joist layout so you buy enough boxes.
Calculators in this family
Frequently asked questions
- How many deck boards do I need?
- Divide the deck area by the coverage of one board and add 10 percent waste. A 12 by 16 foot deck needs about 30 of the 5.5 inch by 16 foot boards.
- How far apart are deck joists?
- 12 or 16 inches on center, with 16 inches standard. Composite decking and diagonal layouts often need 12 inch spacing.
- How many screws for a deck?
- About 350 screws per 100 square feet with 16 inch joist spacing. A 192 square foot deck needs roughly 670 screws.