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Sub-Base Calculator

MOT Type 1 quantity with compaction allowance

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Calculator pre-set for 50mm driveway depth

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Calculator pre-set for 30mm path depth

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Calculator pre-set for 40mm patio depth

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Full 2026 cost breakdown — DIY vs professional

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Sub-Base Calculator

Calculate how much MOT Type 1 sub-base you need for your driveway, patio, or path. Includes automatic compaction allowance so you order the right amount first time.

m
m

Compacted Depth

150mm

Loose Depth Needed

188mm

Volume

2.82m³

Weight

5.64tonnes

Bulk Bags (850kg)

7bags

1-Tonne Bags

6bags

5m × 3m at 150mm compacted depth = 2.82m³ of MOT Type 1, weighing approximately 5.64 tonnes. Order 5.64 tonnes to allow for 25% compaction.

Sub-Base Depth Guide

Recommended compacted depths for different project types. Remember to order extra material to account for 20–25% compaction.

ProjectCompacted DepthLoose Depth (with 25%)Tonnes per 10 m²
Garden path75mm94mm1.88
Patio100mm125mm2.50
Driveway (cars)150mm188mm3.75
Heavy vehicle access200mm250mm5.00

Worked Examples

Standard Driveway

5m × 3m driveway with 150mm compacted sub-base and 25% compaction allowance.

  • Area: 5 × 3 = 15 m²
  • Loose depth: 150 × 1.25 = 188mm
  • Volume: 15 × 0.188 = 2.81 m³
  • Weight: 2.81 × 2.0 = 5.63 tonnes

Garden Path

8m × 1m garden path with 75mm compacted sub-base and 25% compaction allowance.

  • Area: 8 × 1 = 8 m²
  • Loose depth: 75 × 1.25 = 94mm
  • Volume: 8 × 0.094 = 0.75 m³
  • Weight: 0.75 × 2.0 = 1.50 tonnes

Understanding Sub-Base Requirements

MOT Type 1 is the standard sub-base material for UK driveways and patios, specified under Department for Transport Clause 803. It's a crushed aggregate graded from dust to 40mm that compacts into an extremely stable base. The grading means the smaller particles fill the gaps between larger stones, creating a dense, load-bearing layer that distributes weight evenly across the ground beneath.

Why Compaction Matters

MOT Type 1 compacts by 20–25% when properly compacted with a vibrating plate. This means you need to order proportionally more loose material than the final compacted depth. Our calculator includes this allowance automatically. Always compact in layers of no more than 75mm at a time — trying to compact a full 150mm depth in one go won't achieve the required density and leaves a weak spot in the middle.

Type 1 vs Type 3

Type 1 is densely graded for maximum stability — the mixture of fines and coarse aggregate compacts into a near-solid mass. Type 3 is more openly graded with better drainage properties, increasingly specified where SuDS compliance requires the sub-base itself to be permeable. Type 3 is roughly the same price but slightly less stable under heavy loads, making Type 1 the better choice for driveways and areas with regular vehicle traffic.

Now Calculate Your Surface Gravel

Once you know your sub-base quantity, use our main calculator to work out how much decorative gravel you need for the surface layer.

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Frequently Asked Questions

How much sub-base do I need for a driveway?
A standard driveway needs 150–200mm of compacted MOT Type 1 sub-base. For a 30m² driveway at 150mm depth, that's approximately 9 tonnes (after accounting for 25% compaction). Always lay and compact in layers of no more than 75mm at a time.
How much does MOT Type 1 cost?
MOT Type 1 costs approximately £25–£40 per tonne for loose/tipped loads and £50–£70 per bulk bag (850kg). It's one of the cheapest aggregates available because it doesn't need to look decorative — it just needs to be strong.
Can I use Type 1 as a finished surface?
While some people do use MOT Type 1 as a temporary surface, it's not intended for this purpose. The dust-to-40mm grading creates a muddy surface when wet. It's designed as a sub-base only, with decorative gravel, paving, or tarmac laid on top.
Do I need sub-base for a garden path?
For a foot-traffic-only path, 75–100mm of compacted sub-base is sufficient. On very firm ground, you may be able to skip the sub-base for a garden path and lay gravel directly on a weed membrane, but the path won't last as long and may develop dips.
How thick should a sub-base be for a patio?
A patio needs 100–150mm of compacted MOT Type 1, depending on ground conditions. On well-drained, firm soil, 100mm is usually sufficient. On clay or soft ground, go for 150mm to prevent settling.
Can I use crushed concrete instead of MOT Type 1?
Recycled crushed concrete (6F2) is sometimes used as a cheaper alternative and can work well for paths and light-use areas. However, for driveways, MOT Type 1 is recommended as it's specifically graded for load-bearing applications and compacts more reliably.
How do I compact MOT Type 1 properly?
Use a vibrating plate compactor (wacker plate), available from most tool hire shops for around £30–50 per day. Lay material in layers no thicker than 75mm, compacting each layer before adding the next. Water each layer lightly before compacting — it helps the fines bind together.
Do I need a geotextile membrane under sub-base?
On clay or soft soil, yes — a geotextile membrane prevents the sub-base mixing into the ground beneath, which would weaken it over time. On firm, well-drained soil it's less critical but still good practice, especially for driveways.

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