Deck Calculator
Free deck calculator. Enter deck length and width to get the number of deck boards, joists, screws, footings and concrete, plus decking cost.
Deck boards run this direction
- Deck boards
- 29
- 16 ft long
- Linear feet
- 416
- 26 rows
- Deck area
- 192 sq ft
- Decking cost
- $435
Framing and fasteners
| JoistsSize them with a span table | 13 × 12 ft |
| Ledger, rim and end joists | 40 ft |
| Joist hangersLedger side | 13 |
| Deck screwsAbout 3 boxes of 350 | 710 |
| Posts and footingsOne beam, posts about 8 ft apart | 3 |
| Concrete for footings80 lb bags, 12 in × 36 in holes | 12 bags |
Price
$435
Decking boards only, before framing, railing and tax
Default prices are typical U.S. retail figures, reviewed November 2026. Enter your supplier's prices for an exact total.
A deck materials list starts with the decking boards, then works down through joists, the ledger and rim boards, fasteners and footings. The board count depends on board width, the gap between boards and the board length you buy.
Enter the deck size and choose pressure-treated or composite boards. The calculator gives you the boards, linear feet, joists, screws, posts and concrete bags, and prices the decking.
How to use the deck calculator
- Measure the deck length along the house and the width out from the house.
- Divide the width by the board width plus gap to get the number of rows.
- Multiply rows by the length for linear feet, add waste, and divide by board length.
- Divide the length by joist spacing and add one for the number of joists.
- Count two screws per board at every joist.
Rows = width (in) ÷ (board width + gap). Boards = rows × length × (1 + waste) ÷ board length. Joists = length (in) ÷ spacing + 1.
Deck boards needed by deck size
5.5 inch boards with a 1/8 inch gap, 16 ft boards, 10% waste.
| Deck size | Area | 16 ft boards |
|---|---|---|
| 10 × 10 ft | 100 sq ft | 16 |
| 12 × 12 ft | 144 sq ft | 22 |
| 12 × 16 ft | 192 sq ft | 29 |
| 16 × 20 ft | 320 sq ft | 49 |
| 20 × 20 ft | 400 sq ft | 60 |
Tips before you buy
- Choose a board length that matches the deck length, or plan joints so they land on joists and stagger between rows.
- Composite decking often needs 12 inch joist spacing for diagonal layouts; check the manufacturer's span rating.
- Size joists and beams with a span table such as the American Wood Council's DCA 6 guide.
- Footings must go below the frost line in cold climates; ask your building department for the depth.
Frequently asked questions
How many deck boards do I need for a 12x12 deck?
With 5.5 inch boards and a 1/8 inch gap you need 26 rows. That's about 29 boards 12 feet long including 10% waste.
How many screws do I need for a deck?
Two screws per board at every joist. A 12 × 16 deck with joists 16 inches apart needs roughly 700 to 750 screws, or about two boxes of 350.
How far apart should deck joists be?
16 inches on center is standard for wood decking laid straight. Many composite boards and any diagonal layout need 12 inches on center.
What gap should I leave between deck boards?
About 1/8 inch for kiln-dried wood. Wet pressure-treated boards are often laid tight because they shrink as they dry. Composite boards usually need about 3/16 inch; follow the manufacturer.