Shed Base Calculator | MyProjectMate

1. Your measurements

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

Base length

Base width

Concrete thickness

Enter a thickness suitable for your design; this is not a recommendation.

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

Measure the area your shed base needs to cover, not just the shed itself. Choose concrete, paving slabs or both. Edit the thicknesses, product yields and prices to match your actual materials.

The two options are not always suitable substitutes. The shed manufacturer’s base requirements, drainage, ground conditions and expected loads take priority over a price comparison.

What is included?

The estimates cover selected concrete or paving materials, bedding where applicable, and an editable sub-base allowance. They do not include labour, excavation, delivery, edge restraints or reinforcement.

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 shed base

A good shed base starts with the shed manufacturer’s instructions, not a guessed concrete thickness. Use this checklist to plan quantities and identify what still needs checking before buying materials.

Step-by-step overview

Check the shed instructions.Confirm the required base type, footprint, load capacity and any minimum dimensions. A heavy workshop or large shed may need a different foundation from a small lightweight garden shed.

Choose the position.Check access, boundaries, drainage, nearby trees and buried services. Confirm whether planning rules or other permissions affect your project.

Measure the base.Measure length and width in metres. The finished base may need to extend beyond the shed footprint, depending on the manufacturer’s instructions.

Plan the groundwork.Decide on excavation, a suitable compacted sub-base, drainage and any membrane or reinforcement required by the design.

Estimate materials.Use the calculator above. Check concrete bag yield, bulk-bag weight and the actual paving slab dimensions from your supplier.

Build and check level.Follow the selected system’s installation instructions and allow any concrete or mortar to cure appropriately before loading it.

Concrete or paving slabs?

Neither is automatically better. Some shed manufacturers require a solid concrete slab; others permit suitably supported paving. Do not choose purely on the displayed price.

Understanding sub-base estimates

The calculator converts entered depth and density into tonnes. Loose delivery volume, compaction and actual aggregate density can change how much you need. Confirm the supplier’s stated coverage and whether the entered depth is compacted.

Common questions

How much concrete do I need for a 6 × 4 ft shed?

A 6 × 4 ft footprint is about 1.83 × 1.22 m. At an illustrative 100 mm concrete thickness, that is roughly 0.22 m³ before waste. Your required base may be larger and the thickness must suit the design.

Can I put a shed directly on paving slabs?

Only if the shed manufacturer permits that base type and the slabs are properly supported, stable, level and suitable for the loads and ground conditions.

Is ready-mix cheaper than bags?

It can be for larger pours, but minimum orders, delivery, access and pump hire matter. Compare actual supplier quotes, not just a per-m³ price.

Does the estimate include everything?

No. It covers selected materials only. Allow separately for excavation, disposal, delivery, membranes, edge details, reinforcement, labour and tools where needed.