Deck Calculator
Estimate how many deck boards, joists and screws you need for a rectangular deck.
How many deck boards do I need?
Rows = Deck width (in) ÷ (Board width + gap) · Boards = Rows × Deck length × (1 + waste) ÷ Board length
A 16 × 12 ft deck with 5.5 in boards and 3/16 in gaps has 26 rows of boards, each 16 ft long: 416 linear feet. With 10% waste that is 458 ft, or 29 boards of 16 ft. At 16 in on center the deck needs 13 joists, and about 710 deck screws (two per board at each joist).
Joist spacing
Wood decking 5/4 in thick is usually laid on joists 16 in on center; 2× decking can span 24 in. Composite and PVC boards typically require 16 in, and 12 in when the boards run diagonally. Always check the manufacturer's span table, because exceeding it voids most warranties and makes the deck feel bouncy.
Gaps and board length
Leave about 3/16 in between dry boards so water drains and debris falls through. Pressure-treated lumber that is still wet will shrink, so it can be laid tight. Choose board lengths that match the deck length (or half of it) so butt joints land on joists and waste stays low.
Framing size, footings, ledger attachment and railings are governed by local building codes, which usually follow the International Residential Code. Most decks higher than 30 in above grade need a permit.
Frequently asked questions
How many deck boards for a 12×16 deck?
With 5.5 in boards and 3/16 in gaps, about 26 rows. That is 26 boards of 16 ft, or about 29 with 10% waste.
How many screws per deck board?
Two screws at every joist the board crosses. At 16 in on center, a 16 ft board crosses 13 joists, so 26 screws.
What gap should be between deck boards?
About 3/16 in for dry wood and composite. Follow the manufacturer for composite boards, which may specify end gaps for expansion too.
Last reviewed October 2026. Results are estimates; check important decisions with a qualified professional.