Deck Calculator (Boards, Joists & Screws)
Estimate decking boards, joists, screws and stain for a rectangular deck — with board width, gap and joist spacing options.
How to use
- 1Enter the deck length (along the boards) and width.
- 2Choose the board width, gap and joist spacing.
How it's calculated
Rows of boards = width × 12 ÷ (board width + gap). Joists = ⌈length × 12 ÷ spacing⌉ + 1 (running across the boards). Screws ≈ 2 per board per joist. Stain ≈ area ÷ 200 ft² per gallon per coat.
Frequently asked questions
What joist spacing do I need?
16 in on centre is standard for wood decking; composite boards and diagonal layouts often require 12 in. Check the board manufacturer.
What gap should deck boards have?
About 1/8–1/4 in so water drains. Wet pressure-treated boards can be butted tight since they shrink as they dry.
Does this cover structural design?
No — beam and footing sizes depend on spans and local code. Consult your building department or a contractor.