What size paving slabs are most common?

450x450mm and 600x600mm are most popular in the UK. 450mm slabs are easier to handle.

How much wastage for paving?

Allow 10% for cuts and breakages. More for diagonal patterns or complex shapes.

Do I need to account for joints?

For simplicity this calculator assumes tight-fit. With 10mm joints, you need slightly fewer slabs.

What is the best base for paving 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.

Should I lay slabs on sand or mortar?

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.

GardenCalcs

Paving Slab Calculator — How Many Slabs

Calculate how many paving slabs you need for a patio or path.

Length

Length of the patio or path you are paving (measure the longest run)

Width

Width of the paved area across the run

Slab SizeSelect a standard size or enter custom dimensions

Price per Slab (optional)

Cost of one slab — the total cost covers every slab including the wastage allowance

Include 10% wastage

Adds spare slabs on top of the bare minimum so cut offcuts and any breakages don't leave you short

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

Related Calculators

Gravel Calculator

Work out gravel quantities in tonnes or bulk bags for drives and paths.

Patio Area Calculator

Calculate patio area and materials for rectangular or L-shaped patios.

Stepping Stone Calculator

Work out stepping stone quantities and spacing for garden paths.

Block Paving Calculator

Calculate block paving quantities with wastage allowance.

Sand Sub-Base Calculator

Work out sharp sand and sub-base aggregate for paving foundations.

Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.