Paving slab calculator
Convert patio area into a whole-slab buying quantity using slab dimensions and editable waste.
20 LAUNCH TOOLS
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When to use it
Use after measuring the net paved area and selecting the actual single-size slab format and a workable layout.
How it works
Slab area is converted to m²; project area is divided by slab area, waste added, then rounded up.
Worked example
Assume a measured 20 m² patio, 600 × 600 mm slabs and an illustrative 10% cutting allowance. One slab covers 0.6 × 0.6 = 0.36 m²; 20 ÷ 0.36 = 55.556 slabs; 55.556 × 1.10 = 61.111, so round up to 62 whole slabs. Pack sizes may require a second rounding step, and the 10% allowance is not universal.
Measurement guidance
Net paved area in m², actual slab length and width in millimetres, and an allowance chosen for the layout, cuts, breakage and retained spares.
Buying and specification checks
This is an area-based estimate for one rectangular slab size. It does not model joints, actual cut positions, borders, curves, mixed-size packs or drainage; verify the layout and the manufacturer’s pack coverage and sale increment.
Measure, lay out and check the order
A slab total is useful only when the measured area, selected units and intended layout agree.
- Sketch and label the paving footprint, fixed obstacles, doors, drains, edges and excluded beds. Split awkward shapes into traceable parts and keep the net paved area separate from the allowance.
- Use the actual slab dimensions and intended joint width to dry-plan representative rows, borders and visible edges. Calculate different slab sizes or border products separately.
- Choose a cutting and spare allowance for the layout, pattern, site access and your ability to reuse offcuts. A simple rectangular field and a diagonal or heavily cut layout should not inherit an unexplained universal percentage.
- Check the supplier’s pack coverage, pieces per pack, whether stated coverage includes joints, batch availability, delivery access, pallet handling and returns. Round to the sale increment once and keep the same batch for visible work where practicable.
Common mistakes
- Rounding the geometric result down
- Ignoring joints, borders, curves and layout-specific cuts
- Treating mixed-size pack coverage as a simple single-slab count
FREE TOOL AND PROJECT PACK
What the free calculator provides
The free calculator converts net paved area, one rectangular slab size and a visible cutting allowance into a rounded whole-slab estimate. It does not draw the layout, calculate mixed-size packs or approve levels, drainage or the paving system.
What the dedicated pack adds
The Patio Project Pack helps plan and retain the wider ordinary domestic pedestrian-patio project.
- Brief, site, measurement, level, water-route and paving-system decisions before ordering.
- Slab and bulk-material schedules, quote comparison, pack and delivery checks, and an order gate.
- Preparation, laying, troubleshooting, handover, care and a retained patio project passport.
19-page printable digital workbook (PDF). Immediate digital delivery with 90-day access; no subscription.
Practical FAQs
How do I allow for a border in a different slab size?
Measure and calculate the main field and border separately, then test the junction on the layout. Do not combine two sizes into one slab-area input or assume a mixed pack divides evenly.
Does the calculator include joint widths?
No. It divides the net area by the slab face area. Some manufacturer pack coverages include an assumed joint while others quote actual unit coverage, so check the selected product and dry-plan the module before ordering.
What cutting allowance should I use?
There is no single correct percentage. Slab size, pattern, curves, borders, obstacles, breakage, reusable offcuts and the spares you want to retain all matter. Record a reason for the chosen allowance and do not add it again at pack conversion.
Does the slab count confirm the patio layout or drainage?
No. It is an area-based buying estimate. Set out the actual rows, cuts, finished levels and water route separately, and use the selected paving-system instructions and competent advice where site conditions make the detail important.
Planning guidance, not a quotation or a substitute for project-specific design and competent advice.