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Tool: Deck Calculator — Decking Boards, Joists & Screws | Printed on:
Deck Calculator — Decking Boards, Joists & Screws
Calculate decking boards (12', 16', 20'), joist framing (12" or 16" OC), and fasteners.
Project Specifications
Deck Board & Joist Formulas
Transparent mathematical methodology explained in plain English.
Runs = Width / (Board Width + Gap) | Joists = (Length / Joist Spacing) + 2 Calculates the continuous decking lines required across the projection width, linear footage, and joist centers.
Variables Explained:
- Joist Spacing: 16" on center for wood; 12" on center for diagonal or composite.
16 ft × 12 ft Pressure-Treated Deck
Estimating 5/4×6 boards (16 ft length) with 16" joist spacing.
- Effective board width: 5.625 inches (0.46875 ft).
- Decking runs: 12 ÷ 0.46875 = 26 runs.
- Total linear feet: 26 runs × 16 ft = 416 linear ft.
- 16 ft boards needed (with 10% waste): 416 × 1.10 ÷ 16 = 29 boards.
- Joists: (16 ft ÷ 1.33 ft) + 2 = 14 joists.
- Deck screws: 192 sq ft × 3.5 = 672 screws (approx. two 5-lb boxes).
Frequently Asked Questions: Deck Calculator
Click any question below to expand quick answers, formulas, and expert tips.
What gap should be left between deck boards?
For kiln-dried wood or composite decking, leave a 1/8" to 3/16" gap. For wet, pressure-treated lumber, butt boards tightly together because they shrink significantly as they dry.
Professional Advisory: This calculator is for material quantity estimation only. Deck footings, ledger attachment, joist spans, and railing posts must comply with local residential building codes.