Gardeners Toolkit
Whole-patio quantity planner

Patio Materials Calculator

Estimate the quantities in a simple patio build-up: paving slabs, compacted sub-base and bedding volume. Every depth, density and allowance stays visible so you can match the system and supplier you are actually using.

Paving + sub-base + beddingEditable densityQuantity planning, not structural design
Patio build-up cross-section with paving, bedding and sub-base layerspavingbedding layercompacted sub-baseexisting groundchosen sub-base depth

One estimate, with each assumption exposed

This tool calculates quantities from the dimensions you enter. It deliberately does not decide whether a particular sub-base depth, bedding system, mortar ratio or drainage detail is suitable for your site.

Construction specification still matters

Different paving products and sites need different build-ups. Follow the paving manufacturer's installation guidance or professional specification for depth, bedding, falls, drainage and ground conditions.

Estimate patio materials

Start with the finished paved area, then enter the layer thicknesses and supplier assumptions you want to use.

Wastage guide
Step 1

Patio area

Have an L-shape, curve or several patio zones? Measure it with the Garden Area Calculator and enter the total m².

Step 2

Paving slabs

%
Step 3

Compacted sub-base

mm
kg/m³
Editable. Use supplier data where available.
%
Optional. Some supplier guidance applies a separate compaction/order factor; 0% leaves compacted geometry unchanged.

The output keeps compacted geometric volume separate from any extra loose/order factor. This helps avoid hiding compaction inside the maths.

Step 4

Bedding layer

mm

A ratio split is only a theoretical volume breakdown of the bedding volume. It is not a universal mortar specification or bag-yield calculation.

Optional

Simple grid joint-volume estimate

Your patio material estimate

Paving

Area—
Whole minimum—
Order quantity—

Sub-base

Compacted volume—
Order-volume basis—
Approx. weight—

Bedding

Bedding volume—
Sand shareNot split
Cement shareNot split
Planning quantity, not specification

—

Use the estimate in the right order

Check slab count separatelyUse more detailed area and joint options for single-size paving.Review your paving allowanceSimple rectangles and cut-heavy layouts should not be treated as identical.Estimate decorative aggregateFor gravel paths and surfacing rather than compacted patio sub-base.See how assumptions are handledGeometry, units, rounding and supplier overrides.

What this patio materials calculator actually calculates

The tool keeps three different jobs separate: how many paving slabs cover the finished surface, the geometric volume of the compacted sub-base, and the geometric volume of the bedding layer. If you enable optional extras, it can also apply a visible order-volume factor to the sub-base and show a theoretical bedding ratio or simple-grid joint volume.

Layer volume: patio area × finished layer depth = geometric volume. Weight is only an estimate after you apply a density to that volume.
1Paving

Surface coverage and whole slab count.

2Bedding

Chosen installed layer thickness.

3Sub-base

Chosen finished compacted thickness.

4Ground

Site conditions determine the specification.

Compacted volume and loose ordering volume are not the same thing

A 20 m² patio with a 100 mm finished sub-base has a geometric compacted volume of 2.0 m³. That figure describes the finished layer. Real material is delivered loose and then compacted, so suppliers may use a separate compaction or order factor. Marshalls, for example, currently describes applying a compression factor in its sub-base estimating guidance. Rather than hard-coding that into every result, this calculator exposes an optional factor so you can use the figure that suits your material and supplier.

Bedding specifications vary by paving system

Established UK paving suppliers do not all publish the same mortar ratio or layer details across every product. Paving Direct currently describes a 5:1 sharp-sand/cement full bed in its patio guide, while Bradstone publishes a 4:1 example and Marshalls has product-specific guidance. That is exactly why the default result here is bedding volume. If you switch on the ratio split, the ratio is editable and the split remains a theoretical volume calculation, not a universal recipe.

Why jointing is optional

Jointing-product consumption depends on slab dimensions, joint width, joint depth, laying pattern and the product itself. The optional grid estimate models a repeating single-size rectangular grid. For a proprietary jointing compound, the manufacturer's coverage table should take priority.

What this tool does not design

Ground bearingIt does not assess soil strength or movement risk.
Drainage & fallsIt does not design runoff, levels or drainage details.
ExcavationIt does not decide total dig depth or finished levels.
Product suitabilityIt does not decide which paving/bedding system is appropriate.
Research used for this build

Current UK sources reviewed include Marshalls, Bradstone, Paving Direct and Wickes. Their published installation and calculator guidance differs in depth, mix and waste assumptions, reinforcing the decision to keep these inputs editable rather than present one build-up as universally correct.

Continue planning

Paving Slab Calculator →Paving Wastage Guide →Paving & Patios hub →

Unsure how much extra paving to buy?

Use the wastage guide before turning the mathematical slab minimum into an order quantity.

Read the wastage guide
Check the depth & volume referenceVerify litres per square metre and area × depth conversions.