Deck Calculator
Enter your deck size and the board size and this estimates the decking — boards, linear feet, and the joists under them. Material counts only, not a structural design.
Deck boards
30boards
- Decking
- 475 linear ft
- Joists
- 13 joists
This estimates decking boards and joists only — NOT a structural design. Joist size and span, beams, posts, footings, the ledger connection, and railing must follow stamped plans or local code.
How it’s calculated
Rows of decking = ⌈ deck width ÷ board width ⌉ (boards run the length). Decking linear feet = rows × deck length × (1 + waste). Boards = linear feet ÷ board length, rounded up. Joists = ⌈ deck length ÷ spacing ⌉ + 1, spanning the width.
Worked example
A 16 × 12 ft deck with 5½-inch boards, 16 ft long, 16-inch joists, 10% waste: ⌈144 ÷ 5.5⌉ = 27 rows × 16 ft × 1.10 ≈ 475 linear ft = 30 sixteen-foot boards; ⌈16 × 12 ÷ 16⌉ + 1 = 13 joists.
FAQs
- Does this account for the gap between boards?
- It assumes boards laid edge to edge, which slightly over-counts rows once you add the usual ~⅛-inch gap — so it errs toward a few extra boards, which is the safe direction. For a precise count, add the gap to the board width.
- What joist spacing should I use?
- 16 inches on-center is standard; drop to 12 inches for diagonal decking or many composite boards, which need more support. The right spacing and joist size come from the span and the decking — follow your plan and code.
- Does this include the framing and footings?
- No — it counts decking boards and joists only. Beams, posts, footings, the ledger, fasteners, and railing are separate, and their sizing is structural. Use stamped plans or your local code for those.
Sources
- Rows = ⌈deck width ÷ board width⌉; decking lf = rows × length × (1 + waste); boards = lf ÷ board length; joists = ⌈length ÷ spacing⌉ + 1. Material counts only — geometry, not a structural design.