Patio Slab & Pedestal Calculator

What a patio slab calculator has to do

Multiplying square metres by a rule of thumb gives two rough numbers, not an answer. A calculator earns its place only when it turns your real terrace into real quantities:

• Count the whole slabs and the cut slabs at the edges from the real terrace outline — not the area rounded up.
• Work out the pedestal count from the slab grid: a support sits under every joint crossing, with the edges and, for large-format slabs, a centre support included.
• Take the slab format and joint width you actually lay, because the pedestals sit under the joints and the grid sets their positions.
• Return a cut list for the perimeter slabs and the waste percentage, so the order is exact before you buy.

Why the rule-of-thumb numbers are usually wrong

Slabs by area, pedestals by rule of thumb

Most free calculators divide the area by the slab size and assume a flat number of pedestals per square metre. It is fast, but blind to the terrace: it never sees the real grid, so the slab count and especially the pedestal count drift from what the layout needs.

Why the grid sets the pedestal count

Adjustable pedestals sit at the slab corners, so their number follows the grid — one under each joint crossing, plus the supports along the edges. Large-format slabs add a centre support, which a per-square-metre rule cannot see.

Why laying out the terrace is exact

A planner that lays out each slab knows the grid, the edges and the perimeter cuts, so the slab count, the pedestal count and the waste percentage are real for your terrace instead of two rounded guesses.