MOT Type 1 sub-base calculator
Work out how much MOT Type 1 sub-base (also called hardcore) you need under a driveway, patio or shed base. Enter the area and depth and this calculator gives you the weight in tonnes, the bulk bags and the coverage.
MOT Type 1 sub-base calculator
Enter your measurements in metres. Everything updates as you type, and nothing is sent anywhere.
Enter the required compacted depth. The tool assumes 2.1 tonnes per cubic metre of compacted volume, then adds 10% for uneven ground, handling and ordering allowance. That extra is not a second compaction conversion. Bulk bags are assumed to contain 800 kg; confirm the supplier’s density, bag weight and the designed depth for your site.
Worked example: compacted volume to tonnes and bags
For 5 m by 4 m at 100 mm compacted depth, the volume is 20 × 0.1 = 2 m³. At the assumed 2.1 tonnes per m³, that is 4.2 tonnes. The 10% ordering allowance takes it to 4.62 tonnes, or six assumed 800 kg bulk bags after rounding up.
The calculator starts with compacted volume and a compacted-density assumption. Do not then apply another automatic compaction multiplier to the result. The extra 10% is for uneven ground and handling; it is not a measured shrinkage factor for your material.
Suppliers do not all sell the same-weight bulk bag. A six-bag order is only this example’s result when each bag is 800 kg. Ask for the delivered weight, and have the required depth and construction specified for the site rather than choosing them from a quantity tool.
Common questions
How much MOT Type 1 do I need?
Multiply the area by the depth for the volume, then by about 2.1 for the weight in tonnes. At 100mm deep, one tonne of MOT Type 1 covers roughly 5 square metres once compacted. The calculator adds 10% for uneven ground and handling, not an additional compaction conversion.
Is hardcore the same as MOT Type 1?
MOT Type 1 is a graded crushed stone sub-base, and it is what most people mean by hardcore for a modern driveway or patio. It compacts to a solid, level base. Old broken brick and rubble is also called hardcore but does not compact as cleanly, so Type 1 is the standard choice.
How deep should the sub-base be?
About 100mm compacted under a patio or shed base, and 150mm under a driveway that takes a car. Lay and whacker-plate it in layers of no more than 50mm at a time so it compacts properly.
These quantities are a guide to help you order. Always round up and check with your supplier before buying.