How Much Gravel for a Shed Base?

Quick answer: For a gravel shed base, excavate and lay a compacted sub-base of MOT Type 1 about 100mm deep across an area slightly larger than the shed. As a guide, a base for a 2m × 3m shed (6 m²) needs about 1.2–1.3 tonnes of MOT Type 1 at 100mm compacted, plus a compaction allowance. Contain it with timber or a shed-base grid, and level it carefully so the shed sits flat.

A gravel base is one of the best foundations for a shed — it drains well, doesn’t rot, and is far cheaper and easier than a concrete slab — but getting the depth, area, and material right matters, because a shed that sits on a soft or uneven base twists and its doors stop closing. This guide covers how much gravel you need, what type, how deep, and how to build it properly. Use the calculator above to work out your quantity.

Why gravel makes a good shed base

A compacted gravel base has real advantages over other foundations. It drains freely, so water doesn’t pool under the shed and rot the timber floor. It won’t rot or shift the way timber-only bases can. And it’s cheaper and easier than laying a concrete slab, needing no formwork, mixing, or curing time. For most garden sheds, a well-built gravel base is the ideal foundation.

The key is that it must be compacted and level. Loose gravel tipped onto soil isn’t a base — it’ll sink and go uneven, and the shed will twist. The material and method below are what make it solid.

What gravel to use

Use MOT Type 1 — the same crushed-stone sub-base used under driveways and patios. Its mix of stone sizes down to dust compacts into a firm, stable, load-bearing layer, which is exactly what a shed needs. Don’t use loose decorative gravel or pea shingle as the base, because rounded, single-size stone doesn’t lock together and won’t stay firm and level under the shed.

You can finish with a thin layer of decorative gravel on top for looks if you like, but the structural base is MOT Type 1. It’s the compaction of the graded stone that gives you a foundation the shed can sit on without moving.

How deep and how large

For a shed base, lay MOT Type 1 about 100mm deep, compacted. Make the base slightly larger than the shed footprint — extend it 50–100mm beyond each side — so the shed sits fully on firm ground with a small margin, and rainwater running off the roof lands on gravel rather than undercutting the edge.

So for a 2m × 3m shed, build a base of roughly 2.1m × 3.1m. The extra margin also gives you room to sit the shed’s bearers or a frame on solid ground rather than right at the crumbling edge of the base.

Working out the quantity

It’s area × depth × the material’s density. For a 6 m² base at 100mm compacted: 6 × 0.1 = 0.6 m³, and at MOT Type 1’s density (around 2.0–2.1 t/m³) that’s about 1.2–1.3 tonnes. Then add a compaction allowance of around 20–25%, because MOT Type 1 reduces in volume when compacted, so order closer to 1.5 tonnes of loose material.

The calculator applies MOT Type 1’s density when you select it, so enter your base area and 100mm depth, note the tonnage, and add the compaction allowance on top. Remember the base area is slightly larger than the shed itself.

Building it right

Mark out and excavate the area to firm ground, removing turf and soft topsoil. Set an edge — pressure-treated timber, or a purpose-made plastic shed-base grid — to contain the gravel and hold the shape. Fill with MOT Type 1 and compact it in layers with a plate compactor (hireable) to a firm, level surface, checking level with a spirit level and a straight board across the base. A shed-base grid system, filled with gravel, is a popular DIY option that provides containment and a level surface in one.

Getting the base flat and level is the most important part — a shed sitting on an uneven base twists, and doors and windows stop closing properly. Take the time to check the level across the whole base before the shed goes on.

Common mistakes to avoid

The main mistakes are using loose decorative gravel instead of compacted MOT Type 1 (it won’t stay firm), not compacting the base (so it sinks and goes uneven), making the base exactly the shed size with no margin, and forgetting the compaction allowance when ordering. One more: not levelling carefully — an out-of-level base is the usual reason a shed’s doors jam within a season, so it’s worth the extra care.