GardenCalcs.uk
Paving Slab Calculator — How Many Slabs
Calculate how many paving slabs you need for a patio or path.
Length of the patio or path you are paving (measure the longest run)
Width of the paved area across the run
Select a standard size or enter custom dimensions
Cost of one slab — the total cost covers every slab including the wastage allowance
Adds spare slabs on top of the bare minimum so cut offcuts and any breakages don't leave you short
Extra slabs for cuts, breakages and offcuts. 10% suits straight-laid patios; allow 12-15% for diagonal or herringbone patterns and more for curves
How We Calculate This
Slabs = Area ÷ Slab Area, rounded up. When wastage is enabled, the total is increased by your Waste Factor (default 10%) to cover cuts, breakages and offcuts.
Frequently Asked Questions
450x450mm and 600x600mm are most popular in the UK. 450mm slabs are easier to handle. For worked examples and slabs-per-m² tables for every common size, see our how many paving slabs guide.
Allow 10% for cuts and breakages. More for diagonal patterns or complex shapes.
For simplicity this calculator assumes tight-fit. With 10mm joints, you need slightly fewer slabs.
A compacted sub-base of MOT Type 1 (75-100mm) topped with a 30-50mm layer of sharp sand or mortar. This provides a stable, well-drained foundation.
Mortar gives a stronger, more permanent fix ideal for patios. Sand is easier for DIY and allows individual slabs to be lifted later. Use polymeric sand for joints.
Related Calculators
Patio Area Calculator
Calculate patio area and materials for rectangular or L-shaped patios.
Block Paving Calculator
Calculate block paving quantities with wastage allowance.
Jointing Sand Calculator
Calculate kiln-dried or polymeric jointing sand for paving joints.
Sand Sub-Base Calculator
Work out sharp sand and sub-base aggregate for paving foundations.
Path Edging Calculator
Work out edging kerbs or restraints needed for paths and drives.
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Last updated: February 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.