Deck Calculator
The materials list for a deck: deck boards by length, joists, rim and ledger, hangers, screws or hidden clips, beam posts and footing concrete, for composite or wood decking.
Rows of boards = deck depth (in) ÷ (5½ in board + 3/16 in gap); boards = rows × deck width × 1.1 ÷ board length. Joists = width (in) ÷ 16 + 1. A 16 × 12 ft deck needs 26 rows, about 29 boards of 16 ft, 13 joists and about 710 deck screws.
Boards and joists for common deck sizes
16 ft boards with 10% extra, joists 16 in on center.
| Deck | Square feet | Deck boards | Joists | Screws |
|---|---|---|---|---|
| 10 × 10 ft | 100 | 16 | 9 | 416 |
| 12 × 12 ft | 144 | 22 | 10 | 546 |
| 16 × 12 ft | 192 | 29 | 13 | 710 |
| 20 × 12 ft | 240 | 36 | 16 | 874 |
| 16 × 16 ft | 256 | 38 | 13 | 929 |
| 20 × 20 ft | 400 | 60 | 16 | 1,445 |
Before you buy framing
- Joist and beam sizes depend on span, species and load. Size them from the span tables in the American Wood Council's DCA 6 deck guide or your local code.
- Composite boards often require 12 in joist spacing for diagonal decking or stairs; check the maker's installation guide.
- Footings must reach below the frost line, and ledgers need through-bolts or structural screws into the house rim joist, never nails.
- Building stairs off the deck? Use the stair calculator.
Frequently asked questions
How many deck boards do I need?
Divide the deck depth in inches by the board width plus gap (5½ in + 3/16 in for most boards) to get the number of rows, multiply by the deck width in feet for linear feet, add 10% and divide by the board length.
How many joists do I need for a deck?
Deck width in inches ÷ joist spacing (usually 16 in), plus one. A 16 ft wide deck needs 13 joists at 16 in on center, or 17 at 12 in.
How many screws do I need for a deck?
Two screws per board at every joist. For a 16 × 12 ft deck with 26 rows and 13 joists, that is about 680 screws plus a few extra. A 5 lb box of 2½ in deck screws usually holds around 350–400.
What is the gap between deck boards?
About 3/16 in for most wood and composite boards, enough for water to drain. Composite makers specify their own gaps for end-to-end joints and temperature; follow the installation guide.
How deep should deck footings be?
Below your local frost line and at least 12 in deep in warm climates. Footing size depends on the load each post carries; the AWC DCA 6 guide and local code give the minimums.
Run a garden club, nursery or landscaping site? Embed this calculator free with one line of code.
Related free tools
Stair Calculator
Risers, treads, stringer length and code checks for any total rise.
Open tool →Stair Stringer Calculator
Cut layout, stringer length, throat depth and how many stringers.
Open tool →Board Foot Calculator
Board feet, linear feet and cost for a lumber list.
Open tool →Log Board Foot Calculator
Board feet in logs by Doyle, Scribner and International ¼ in.
Open tool →Sources and assumptions
Board layout assumes 5½ in wide boards with a 3/16 in gap and 10% waste. Joist spacing, ledger, footing and framing guidance points to the American Wood Council DCA 6 deck guide; this calculator does not size joists or beams. Footings are 12 in × 36 in by default. Prices are placeholders to edit.