About this calculator
Deck boards are sold by the piece, and the count depends on the board width, the gap you leave between boards and how the board lengths fit the deck. This calculator works out how many rows of boards cover the deck, converts that into linear feet and full-length boards with a waste allowance, and counts face screws at two per joist.
It works for pressure-treated pine, cedar, hardwood and composite or PVC decking.
How to use it
- Enter the deck’s length in the direction the boards run (usually parallel to the house) and its width across the boards.
- Choose the actual board width — a nominal 2×6 or 5/4×6 is 5½ in wide.
- Enter the gap between boards and the board length you’ll buy.
- Choose the joist spacing and keep 10% extra for end cuts and rejected boards.
The formula
Rows = deck width ÷ (board width + gap), rounded up
Linear feet = rows × deck length
Boards = linear feet × (1 + extra%) ÷ board length, rounded up
Screws = rows × joists × 2
A 5½ in board with a 3/16 in gap covers 5.69 in of deck, so each foot of deck width needs about 2.1 rows of boards.
Worked example
These are the calculator’s starting values and the results they produce:
| Deck length (direction boards run) | 16 ft |
|---|---|
| Deck width (across the boards) | 12 ft |
| Board width (actual) | 5½ in (5/4×6 or 2×6) |
| Gap between boards | 0.1875 in |
| Board length | 16 ft |
| Joist spacing | 16 in on center |
| Extra for cuts and defects | 10 % |
Tips before you buy
- Choose board lengths that span the deck without joints where possible, or plan staggered butt joints that land on doubled joists.
- Wet pressure-treated boards shrink as they dry — many builders install them tight and let the gap open up.
- Composite decking often requires 12 in joist spacing when boards run diagonally; check the manufacturer’s span table.
- Pre-drill near board ends to prevent splitting.
Frequently asked questions
How many deck boards do I need for a 12×16 deck?
With 5½ in boards and 3/16 in gaps running the 16 ft length, you need 26 rows. That’s 416 linear feet, or 29 boards 16 ft long with 10% extra.
How many screws do I need for decking?
Two screws per board at every joist. A 12 × 16 ft deck with joists 16 in on center has 13 joists under each row, so 26 rows need 676 screws.
How wide is a 5/4 deck board?
A 5/4 × 6 deck board is actually about 1 in thick and 5½ in wide. A 2 × 6 is 1½ in thick and also 5½ in wide.