Check the path
Your calculation audit
Every total is shown as a short sequence so you can see what was measured, deducted, adjusted and rounded.
- 01Awaiting valid measurementsComplete the fields above to reveal the formula path.
Paving & Decking
Decking calculator
Estimate deck boards and packs from finished deck area, board size, board gap and waste.
Transparent formulaFormula v1.0 · deck area ÷ board length × (board width + gap) × waste allowance
Scope boundary: Surface-board estimate only — it does not design joists, supports, foundations, drainage or structural loads.
Measure clearly
Simple guidance
Measure the finished deck surface. Use the actual board length and width, then enter the installed board gap so the calculator can estimate each board's effective coverage.
Worked example
Follow the same logic
A 12 m² deck using 3.6 m × 145 mm boards with a 5 mm gap has an effective board coverage of 0.54 m² before the selected cut allowance and pack rounding.
Planning tipWrite down the product factor or pack size you used, so a later change is easy to trace.
Before you buy
Three quick checks
- 01
Measure the finished deck surface, excluding steps or areas without boards.
- 02
Use the exact board length and width you intend to buy.
- 03
Confirm pack count, cut layout and product-specific installation gaps before ordering.
Quick answers
Useful to know
Why does the board gap change the result?
The gap is part of the installed coverage across the board width. It changes how much finished surface one board represents.
Does this calculate joists or supports?
No. It estimates surface boards only and does not design joists, supports, foundations, drainage or structural loads.
Review record
Transparent, source-ready method
Last reviewed: 15 October 2026. Formula version: v1.0. Source/review data to be added — Calculator.Shop does not present placeholder figures as an authoritative trade specification.