How the deck calculator works
Rows of boards = deck width (in) ÷ (board width + gap), rounded up
Boards = rows × boards per row × (1 + waste)
Joists = deck length (in) ÷ joist spacing + 1 · Screws = rows × joists × 2
Example: a 16 × 12 ft deck with 16 ft boards
12 feet is 144 inches, and each board plus gap takes 5.625 inches, so you need 26 rows. Each row is one 16 ft board, and with 10% extra that's 29 boards, about $725 at $25 each. Joists 16 inches apart across 16 feet means 13 joists, and two screws per board at every joist comes to 676 screws.
What this doesn't cover
Beams, posts, footings, ledger, railings and stairs depend on your design and local code. Have the framing checked or permitted before you build.
Frequently asked questions
How many deck boards do I need?
Divide the deck width in inches by the board width plus the gap to get rows, then multiply by the boards needed to span each row. Add about 10% for waste.
How many screws per deck board?
Two at every joist. On a deck with joists 16 inches apart, that's about 350 screws per 100 square feet.
Last reviewed: 2026-10-31