Patio Slab Calculator | MyProjectMate

1. Your patio measurements

Measure the base you intend to build, which may be larger than the shed footprint. All measurements are editable.

Base length

Base width

Extra allowance

Optional allowance for variation and wastage.

Number of post holes

holes

Hole diameter

Concrete fill depth

Post width (square)

Assumes cylindrical holes and a centred square post. The entered depth is the concrete-filled depth. Confirm the required hole size and installation method for your fence.

2. Base options

Choose which estimates you want to see. Turn either option off to hide its inputs and results.

Concrete basePaving slab base

3. Concrete buying assumptions

Premixed bag size

Concrete yield per bag

The 10 L yield is an illustrative starting assumption, not a universal specification. Check the exact yield stated by your chosen product.

Price per bag

Ready-mix price per m³

Both prices are placeholders. Ready-mix delivery, minimum order, pump charges and VAT treatment may change the quote.

4. Shared groundwork assumptions

Enter suitable depths based on the manufacturer's instructions and site conditions. The calculator does not determine what construction is safe.

Sub-base depth

Sub-base density

t/m³

Sub-base bulk bag content

Price per sub-base bulk bag

5. Paving slab assumptions

Slab length

Slab width

Price per slab

Bedding layer depth

Bedding material density

t/m³

Bedding bulk bag content

Price per bedding bulk bag

All default prices, densities, yields and bag sizes are illustrative. Check actual product specifications, including whether bedding requires a particular mortar mix rather than loose sand.

Joint width between slabs

Used for a simple straight rectangular grid. Cuts and patterns are not modelled.

Your materials estimate

Base area—Both options use the same base footprint

Concrete base

—

Estimated bagged concrete + sub-base

Concrete—

Premixed bags—

Ready-mix alternative*—

Paving slab base

—

Estimated slabs + bedding + sub-base

Slabs—

Bedding—

Sub-base—

*Ready-mix figure is concrete-only; it excludes the sub-base, delivery, minimum order and other fees. This is not a direct comparison with the paving total.

Printable shopping lists

Concrete option

Paving slab option

All totals are estimates of selected materials only, not supplier quotations. Labour, plant hire, delivery, VAT differences, edge restraints, drainage, membranes, reinforcement, fixings and site preparation are excluded.

Before you buy

Important: Concrete thickness, base preparation, reinforcement, drainage and ground suitability depend on the shed, its loads and local conditions. Follow the shed manufacturer's requirements and seek qualified advice where appropriate. Do not rely on this calculator to decide structural specifications.

The two shed-base options are not structurally interchangeable in every situation. Patio layouts and joint widths can change slab counts. Fence-hole dimensions depend on the ground, fence design and exposure. Verify product yields, material suitability and installation methods before ordering. Affiliate links, if added, will be clearly disclosed.

How to use this calculator

Enter your patio length and width, then the dimensions of your chosen slabs. The calculator uses a rectangular grid with your entered joint width, adds your waste allowance, and estimates bedding and sub-base quantities.

Real patio layouts can need extra slabs for cuts, corners and laying patterns. Confirm bedding materials and depth against the paving manufacturer’s instructions, particularly where a mortar bed is required.

Prices and material properties are example starting values, not live supplier quotes. Always check bag yields, dimensions, delivery costs and suitability before ordering.

How to plan a garden patio

Patio materials depend on the paving product, ground conditions, drainage and laying method. This guide helps you turn measurements into a sensible shopping list.

Step-by-step overview

Measure the full paved area.Record the overall length and width. For L-shaped patios, calculate each rectangular section separately and add the quantities.

Choose your paving.Check the exact slab size, thickness, recommended joint width and the manufacturer’s laying instructions.

Plan levels and drainage.Work out how surface water will drain safely away from buildings and neighbours. Check whether the patio needs a drainage solution or permissions.

Specify the layers.Choose the appropriate sub-base, compaction, bedding system and edge restraints for the paving and expected use.

Allow for cuts and breakages.A simple grid estimate cannot predict every cut, pattern or reusable offcut. Add a realistic waste allowance for your layout.

Check a trial layout.Dry-lay or sketch the pattern, including joint widths and edge cuts, before ordering.

Why slab counts vary

Our calculator counts rectangular grid positions and then adds your waste allowance. Herringbone patterns, staggered layouts, irregular edges and reused offcuts can change the actual number.

Bedding is product-specific

Not all slabs can be laid on the same bedding material. Some paving systems require a full mortar bed, bonding slurry and particular jointing products. Follow the paving manufacturer.

Common questions

Does the calculator include gaps between slabs?

Yes. The entered joint width is included in the simple rectangular grid count, but it does not model a detailed cutting plan.

Can I lay slabs straight onto soil?

That is generally unsuitable for a durable patio. Ground preparation, a suitable foundation and the correct bedding system matter.

How much extra paving should I order?

The right allowance depends on the shape, pattern, breakages and cutting. The adjustable percentage is a planning input, not a universal recommendation.

Is a 40 mm bedding layer always correct?

No. The default is an example only. Use the bedding thickness and material required by your paving system and site conditions.

Need a base for a shed instead? Use the shed base calculator.