Garden Surveyor
How to work out MOT Type 1 quantities
MOT Type 1 (also called Type 1 sub-base or hardcore) is the compacted stone layer that sits under patios, driveways, paths and shed bases. To estimate it, take your area in square metres, multiply by the finished compacted depth in metres, add about 25% for compaction, and convert to tonnes using a density of roughly 2.1 tonnes per cubic metre. The calculator above does all of this and rounds up to whole bulk bags so you order enough to finish.
Recommended sub-base depths (UK)
| Job type | Compacted depth |
|---|---|
| Garden / informal path (pedestrian) | 75 mm compacted |
| Artificial grass sub-base | 75 mm compacted |
| Patio / footpath | 100 mm compacted |
| Shed / outbuilding base | 100 mm compacted |
| Gravel area / gravel driveway | 100 mm compacted |
| Domestic driveway (cars) | 150 mm compacted |
| Resin-bound / tarmac sub-base | 150 mm compacted |
| Heavy / commercial driveway (vans) | 200 mm compacted |
Lay and compact in lifts of no more than 100 mm at a time. Over soft or clay ground, add depth and a geotextile separation membrane to stop the sub-base sinking into the subgrade.
Pricing the whole job, not just the stone?
Set out levels and falls, take off every material and build a compliance-aware quote.
Frequently asked questions
- How much MOT Type 1 do I need?
- Multiply your area (m²) by the compacted depth (m), then multiply the compacted volume by about 1.25 to allow for compaction, and by roughly 2.1 tonnes per m³ for MOT Type 1. The calculator does this for you and converts the result into tonnes, bulk bags and 25 kg bags.
- What depth of sub-base do I need?
- As a UK rule of thumb: 75 mm compacted for pedestrian paths and under artificial grass; 100 mm for patios, footpaths, shed bases and gravel areas; 150 mm for domestic driveways (cars) and as a base for resin-bound or tarmac; and 200 mm for heavy or commercial driveways taking vans. Soft or clay subgrades may need more depth plus a geotextile separation membrane.
- How many tonnes is a bulk bag of Type 1?
- A standard bulk (jumbo) bag of MOT Type 1 holds roughly 0.85 tonnes. The calculator rounds up to whole bags so you order enough to finish the job.
- Why is loose volume bigger than compacted volume?
- MOT Type 1 is delivered loose and reduces in volume once it is whacked down with a plate compactor. We add about 25% to the finished (compacted) volume so you buy enough loose material to compact to your target depth.
- Does this work for a driveway sub-base?
- Yes. Choose the driveway purpose (150 mm) or set your own compacted depth. For heavier use or poor ground, increase the depth and lay in compaction lifts of no more than 100 mm at a time.