Deck Calculator
Work out the decking boards, joists and screws for a new deck. Enter the deck size, the board width and length, and the joist spacing to get a shopping list for the deck surface.
- Rows of boards
- 26
- Linear feet of decking
- 416 ft
- Joists
- 13 × 12 ft
- Deck screws (approx.)
- 676 screws
- Deck area
- 192 sq ft
How this calculator works
Boards run along the length of the deck. The number of rows is the deck width divided by the board width plus the gap between boards, rounded up.
If the deck is longer than one board, each row needs several boards. Joists run across the deck, so their number is the deck length divided by the joist spacing, plus one.
Screws assume two per board at every joist. The calculator covers the deck surface and joists only — beams, posts and footings depend on your structural design.
Example: a 16 × 12 ft deck with 5.5 in boards
- Board plus gap: 5.5 + 0.125 = 5.625 in.
- Rows: 12 ft × 12 = 144 in ÷ 5.625 = 25.6, so 26 rows.
- With 16 ft boards, each row is one board: 26 boards, or 29 with 10% extra.
- Joists at 16 in on center: 192 in ÷ 16 = 12, plus one = 13 joists.
- Screws: 26 rows × 13 joists × 2 = 676 screws.
Quick reference
| Deck size | Rows | Boards (one board per row) |
|---|---|---|
| 10 × 10 ft | 22 | 25 × 10 ft |
| 12 × 12 ft | 26 | 29 × 12 ft |
| 16 × 12 ft | 26 | 29 × 16 ft |
| 20 × 16 ft | 35 | 39 × 20 ft |
Tips before you buy
- Pick a board length that matches the deck length (or divides it evenly) to reduce waste and avoid butt joints.
- Composite boards often need specific gaps and joist spacing — 12 in on center for diagonal installs is common. Follow the manufacturer.
- Order a few extra boards from the same batch; color can vary between lots.
Frequently asked questions
How many deck boards do I need for a 12 × 12 deck?
With 5.5 inch boards and a 1/8 inch gap, a 12 × 12 ft deck needs 26 rows. Using 12 ft boards that is 26 boards, or about 29 with 10% extra for cuts.
How far apart should deck joists be?
Joists are usually 16 inches on center for wood and most composite decking. Diagonal decking and some composite products require 12 inches.
How big a gap should I leave between deck boards?
About 1/8 inch for kiln-dried or composite boards. Wet pressure-treated boards can be installed tight, because they shrink as they dry.
Related calculators
Last updated October 25, 2026