How to calculate deck boards
- Divide the deck width (in inches) by the board width plus a 3/16 in gap to get the number of rows.
- Divide the deck length by the board length to see how many boards each row needs.
- Multiply rows × boards per row and add 5–10% for waste and bad boards.
A 16 × 12 ft deck with 5.5 in boards has about 26 rows. With 16 ft boards, that’s 26 boards plus waste — about 29.
Joist spacing
| Decking | Maximum joist spacing (typical) |
|---|---|
| 5/4 wood boards | 16 in on center |
| 2× wood boards | 16–24 in |
| Composite / PVC | 12–16 in — check the manufacturer |
| Diagonal decking | 12 in |
Always follow your decking manufacturer’s span rating and your local building code — joist size, beam spans, footings and ledger attachment are usually inspected.
Fasteners
Face-screwing uses two screws at each joist, roughly 350 screws per 100 sq ft at 16 in spacing. Hidden fastener clips are usually sold by deck area; one box often covers about 50–100 sq ft.
Planning tips
- Choose board lengths that match your deck length to avoid butt joints — or stagger joints over joists.
- Leave gaps for drainage and expansion (wood shrinks, composite expands with heat).
- Footings are concrete — size them with the concrete calculator, and plan a railing or fence with the fence calculator.
Frequently asked questions
How many deck boards do I need for a 12×16 deck?
About 26–29 boards that are 16 ft long and 5.5 inches wide, including waste.
What is the standard joist spacing for a deck?
16 inches on center for most wood and composite decking.
How much gap should be between deck boards?
About 1/8 to 1/4 inch; 3/16 inch is common.
How many screws per deck board?
Two screws at every joist, roughly 350 per 100 square feet.