Free MOT Type 1 & Sub-Base Calculator | DigFill

## The Hidden Cost of Aggregate Compaction When ordering sub-base materials like MOT Type 1 for a driveway, patio, or path, the most common mistake is ordering based purely on flat geometry. If you need a 150mm deep sub-base, ordering exactly 150mm worth of loose aggregate will leave you short. Why? Because aggregates must be heavily compacted (usually with a vibrating wacker plate or roller) to provide a stable, load-bearing foundation. ### Understanding Compaction Factors Different materials compress at different rates when laid and tracked down: * **MOT Type 1:** The UK standard for hardcore sub-bases. It consists of crushed stone and dust that locks together perfectly. Type 1 has a compaction factor of **~20%**. This means you must order 20% *more* loose volume to hit your target compacted depth. * **MOT Type 3:** A reduced-fines aggregate used for permeable paving and SUDS (Sustainable Drainage Systems). Because it has fewer fine particles to fill the voids, it compacts slightly less than Type 1. * **Sharp Sand:** Typically used as a screed or laying course under block paving. It requires a smaller compaction allowance but is denser than crushed stone. Our calculator automatically applies the correct compaction factor based on your selected material, ensuring you order the exact amount of loose tonnes required to achieve your finished, compacted depth. --- ## Explore More Site Tools

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