How much bigger should a shed base be than the shed?

A shed base should extend 50-100mm beyond the shed on each side. This gives a small overhang that prevents water dripping directly off the roof onto the base edge, which can cause erosion and undermine the base. For a 6×4 foot shed (1.83×1.22m), make the base roughly 1.98×1.37m with a 75mm overhang all round.

What is the best type of base for a shed?

A concrete slab is the strongest and most durable option, ideal for larger sheds and workshops. Paving slabs on a sand bed are easier for DIYers and work well for smaller sheds. A gravel pad with timber frame is the quickest and cheapest option, and works well for standard garden sheds. All options need a compacted Type 1 sub-base for stability.

How thick should a concrete shed base be?

A concrete shed base should be at least 75-100mm thick for a standard garden shed. For larger workshops or sheds storing heavy equipment, go for 150mm. Always lay concrete on a compacted 100mm Type 1 sub-base. Use our Concrete Volume Calculator (/structural/concrete-volume-calculator) for detailed concrete quantities.

Do I need planning permission for a shed base?

In most cases you don't need planning permission for a shed base in your garden, as sheds fall under permitted development rights. However, if your shed is in a conservation area, covers more than 50% of your garden, or exceeds certain height limits, you may need permission. Check with your local council planning department if unsure.

How many paving slabs do I need for a shed base?

The number depends on your shed size and slab size. For 600×600mm slabs, divide your base area by 0.36 m² per slab. For a 6×4 foot shed (about 2.0×1.4m base with overhang), you need approximately 8 slabs using 600×600mm pavers. This calculator works it out including wastage. For more paving options, see our Paving Slab Calculator (/landscaping/paving-slab-calculator).

Shed Base Calculator — Concrete, Slabs & Gravel Pad UK

Shed Base Calculator — Materials for Concrete, Slabs or Gravel

Calculate the exact materials you need for a shed base — whether concrete slab, paving slabs or a gravel pad.

Shed Length

External length of your shed

Shed Width

External width of your shed

Base Type

Choose your preferred base construction

Slab Thickness

75-100mm for standard sheds

Overhang Each Side

Base extends beyond shed (50-100mm recommended)

Wastage Allowance

10% recommended for most projects

How We Calculate This

This calculator works out the materials needed for your shed base. It adds an overhang around the shed (default 75mm each side) to give the base proper weather protection, then calculates materials based on your chosen base type.

Base size formula

Base Length = Shed Length + (2 × Overhang)
Base Width = Shed Width + (2 × Overhang)
Base Area = Base Length × Base Width

Concrete slab

Volume (m³) = Base Area × Thickness
Each 25kg premix bag yields approximately 0.012 m³. For site-mixed concrete (1:2:3 ratio), we calculate ~320kg cement, ~640kg sand, and ~960kg aggregate per m³ of concrete.

Paving slabs

Slabs needed = Base Area ÷ Individual Slab Area
Laid on a 30mm sharp sand bed over 100mm compacted Type 1 sub-base.

Gravel pad

Gravel (tonnes) = Base Area × Depth × 1.7 t/m³
Gravel is contained within a timber frame and laid on weed membrane.

All calculations include an editable wastage allowance (default 10%) and all options include a 100mm Type 1 sub-base where appropriate.

Frequently Asked Questions

Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Shed Base Calculator — Materials for Concrete, Slabs or Gravel

How We Calculate This

Base size formula

Concrete slab

Paving slabs

Gravel pad

Frequently Asked Questions

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