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
Paving & decking calculator
Estimate paving slabs or deck boards from project area, material size, layout waste and packs.
Transparent formulaFormula v1.0 · project area ÷ effective unit area × layout allowance
Scope boundary: No structural, drainage or ground-preparation approval is provided by this materials estimate.
Measure clearly
Simple guidance
Measure the finished patio or deck footprint. For decking, record board spacing as well as board size; for paving, set spacing to zero and add a layout allowance.
Worked example
Follow the same logic
A 12 m² patio using 600 × 600 mm slabs needs about 33.3 slabs 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 surface, excluding areas that will not be covered.
- 02
Use actual slab or board sizes, not nominal product names.
- 03
Confirm pack contents and layout cuts before ordering.
Quick answers
Useful to know
Does this calculate drainage or a deck structure?
No. It estimates surface materials only and does not assess drainage, sub-base, supports, joists or structural loads.
Should I include board spacing?
For decking, use the intended board gap. For paving slabs, set the board-spacing field to zero and use the waste allowance for cuts.
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.