Inputs
Results
Enter your deck dimensions then click Calculate.
NAIBC / IRC codes
References & Sources
Standards Cited
- AWC DCA 6 — American Wood Council Prescriptive Residential Wood Deck Construction Guide
Provides guidance on joist spacing, board thickness, gap sizes, and structural requirements for timber decking - AWPA U1 — Use Category System: User Specification for Treated Wood
Guidance on timber treatment and preservation for external decking exposed to weather
Formulas Used
- Deck Area:
A = deckWidth x deckLength
Source: Standard geometry - Boards Across Width:
boards = ceil((deckWidth_mm + gapSize) / (boardWidth + gapSize))
Source: AWC DCA 6 decking guidance — Effective board width includes the gap between boards - Joists Required:
joist bays = ceil(deckLength_mm / maximum spacing); joists = bays + 1
Source: AWC DCA 6 decking guidance — Bays are redistributed equally so both ends and every calculated board joint are supported - Screws Needed:
screws = boardsAcross x (joistsRequired + supportedButtJointsPerStrip) x 2
Source: AWC DCA 6 decking guidance — 2 screws per board per joist intersection - Linear Metres of Board:
linearMetres = boardsNeeded x deckLength
Source: Standard calculation
Key Assumptions
- Recommended joist spacing: 300mm for boards <20mm thick, 400mm for <25mm, 450mm for <32mm, 600mm for >=32mm — AWC DCA 6 decking guidance
- Gap between decking boards typically 3-6mm for drainage and expansion — AWC DCA 6 decking guidance
- 10% wastage allowance for cuts at board ends — Industry standard practice
- 2 screws per board at each joist crossing point — AWC DCA 6 decking guidance