Decking Material Calculator
Deck size + board width + gap + joist spacing → deck boards, joists, beams, and screws/fasteners.
Result
- Deck size16 × 12 ft = 192 ft²
- Board width5.5"
- Gap0.125"
- Effective cover per row5.625"
- Board rows across width26
- Boards needed (with waste)29 × 16-ft
- Total linear ft of decking464 lft
- Joists (across width)13
- Beams (1 per 8 ft length)2
- Deck screws (#10 × 2.5")2489
Step-by-step
- Effective row cover = 5.5 + 0.125 = 5.625".
- Board rows = ⌈144 / 5.625⌉ = 26.
- Boards (with waste) = ⌈26 × 1.10⌉ = 29.
- Joists = ⌈192 / 16⌉ + 1 = 13 (each ~12-ft long).
- Screws ≈ 29 boards × 13 crossings × 6 screws × 1.10 = 2489.
How to use this calculator
- Enter deck length and width.
- Enter board width and gap.
- Pick joist o.c. spacing matching the deck-board material.
- Adjust waste — 10% standard.
About this calculator
Deck framing typically uses pressure-treated 2x lumber at 16" on-center joist spacing for traditional lumber decks; 12" o.c. for composite decking due to lower stiffness. Boards run perpendicular to joists, with a ⅛" gap between them for drainage and wood-movement. Deck screws are typically #10 × 2.5", driven 2 per joist crossing for traditional lumber (6 per 12-ft board on a 16" o.c. frame), and hidden-fastener systems for composite.
What this calculator does
This calculator computes the materials needed to build a rectangular deck: deck boards (count and total linear feet), joists (across the deck width), beams (1 per ~8-ft length), and deck screws. The board count uses effective row coverage (board width + gap) divided into the deck width; joist count uses length divided by on-center spacing.
How it works — the formula
effective_cover = board_width + gap (in)
board_rows = ⌈deck_width_in / effective_cover⌉
boards = ⌈board_rows × (1 + waste)⌉
joists = ⌈deck_length_in / OC_spacing⌉ + 1
screws ≈ boards × joists × 6 × (1 + waste)Each board runs the full deck length; one row of boards spans (board_width + gap) of deck width. Joists run across the deck width at the chosen on-center spacing, with +1 for end joists. Screws assume 2 per joist crossing × 3 ft per joist span ≈ 6 per board per crossing (industry rule of thumb).
Worked examples
- Inputs:
- L=16, W=12, board=5.5, gap=⅛, OC=16, waste=10%
- Output:
- ~29 boards (16-ft) + ~13 joists + ~2270 screws
Standard residential deck.
- Inputs:
- L=20, W=16, board=5.5, gap=¼, OC=12, waste=10%
- Output:
- ~39 boards + ~21 joists + ~4910 screws
Composite requires 12" o.c. and slightly more gap.
- Inputs:
- L=12, W=10, board=5.5, gap=⅛, OC=16, waste=15%
- Output:
- ~24 boards + ~10 joists + ~1440 screws
Higher waste for picture-frame perimeter cuts.
When to use this vs other tools
Use this for new-deck materials estimating. For existing-deck math, the related tools cover area, cost, and other downstream calculations.
- Deck Square Footage
Use to compute area for an existing odd-shaped deck.
- Deck Material
Use for material-quantity rules of thumb (predecessor to this fuller estimator).
- Deck Build Cost
Use to convert materials into dollars for total project budget.
Authority note
DCA 6 is the AWC publication referenced by every US residential deck code (IRC R507). It codifies joist spacing, ledger attachment, post sizing, and fastener requirements used here.
Limitations
- Rectangular decks only. Wraparound and multi-level decks need section-by-section take-off.
- Excludes posts, footings, beams beyond the simple per-8-ft estimate, railings, stairs, and balusters.
- Screw count is a rule of thumb; hidden-fastener systems for composite need separate take-off.
- Joist span limits from DCA 6 are not enforced here — verify for your lumber size and spacing.
Residential decks must comply with IRC R507 and local amendments. Pull a permit and have engineering oversight for any deck attached to a habitable structure.