MOT Type 1 & Aggregate Calculator (UK)

Standard UK guidance: 75 mm minimum for a foot-traffic patio, 100 mm for a light domestic driveway, 150 mm for a regular driveway carrying a family car, 200 mm for heavy domestic use or a shared driveway, and 250–300 mm for commercial-vehicle traffic. The 150 mm depth is what most DIY guides default to. If you're on soft clay or made-up ground, add 50 mm. The block paver or slab sits on top of this layer, usually bedded on a 50 mm sharp-sand course.

One tonne of MOT Type 1 covers approximately 4.76 m² at 100 mm depth, 6.35 m² at 75 mm, or 3.17 m² at 150 mm. The maths: MOT Type 1 has a compacted density of roughly 2.1 t/m³, so 1 tonne is around 0.476 m³ — divide by your depth in metres to get coverage area. Loose density before compaction is lower (about 1.7 t/m³), so when ordering you should add 15–25% to allow for compaction.

A standard UK builders' bulk bag (also called a "dumpy bag" or "tonne bag") holds 0.7 to 0.8 tonnes of MOT Type 1 — most suppliers quote 0.8 tonnes as the working figure, but it varies by quarry. So three bulk bags is roughly 2.4 tonnes, four bags is about 3.2 tonnes. If you're ordering by the bulk bag, always add an extra one for waste. For larger jobs (over 5 bulk bags), a tipped tonnage delivery direct from a quarry usually works out cheaper per tonne.

MOT Type 1 is a graded crushed limestone or granite aggregate (max 63 mm) used for sub-base under driveways, paths and patios — it locks together when compacted and gives a stable load-bearing layer. Type 3 is similar but has tighter grading (max 40 mm) and is designed to be permeable — water drains through it rather than running off, which is required by SUDS regulations on many new builds. For most domestic DIY work, Type 1 is the default. Use Type 3 where you need permeable paving.

"Hardcore" is a loose term — historically it meant crushed brick, broken concrete or crushed stone used as fill. In modern UK construction, MOT Type 1 has largely replaced traditional hardcore for any structural use. For volume calculations, treat hardcore as roughly 1.8–2.0 t/m³ density. Type 1 hardcore specifically is a synonym for MOT Type 1 and runs at 2.1 t/m³ compacted. Always over-order by 10–20%.

MOT Type 1 is a granular sub-base material specified by the Department for Transport in the Specification for Highway Works Series 800 (clause 803). It's a well-graded crushed rock (typically limestone, granite or basalt) with a maximum particle size of 63 mm and a controlled distribution of finer particles down to dust. When compacted, the fines fill the gaps between larger stones, creating a dense, stable, load-bearing layer. It's the standard sub-base for UK roads, driveways and pavements.

Yes — uncompacted MOT Type 1 is significantly weaker than compacted Type 1, and your driveway will settle and rut within months. Spread the Type 1 in layers no thicker than 100 mm at a time, then compact each layer with a wacker plate — at least four passes in different directions per layer. For larger areas, hire a small roller. Lightly wetting the Type 1 with a hose during compaction helps the fines bed down properly.

Not directly — block paving needs a 30–50 mm bedding course of sharp sand on top of the compacted Type 1. The pavers are laid into this sand, vibrated in with a wacker plate fitted with a rubber pad, and the joints are filled with kiln-dried jointing sand. The Type 1 provides the structural foundation; the sand provides the bedding tolerance. For a 100 mm Type 1 + 50 mm sand + ~50 mm paver build-up, you're looking at roughly 200 mm dig-out below your finished level.

Three options. (1) Bulk bags from a builders' merchant — convenient for small jobs, around £50–£80 per bag including delivery. (2) Loose tipped delivery from a local quarry — much cheaper per tonne but you need somewhere flat for the tipper, minimum order usually 5–8 tonnes. (3) Grab lorry — works for medium jobs (3–6 tonnes) and the operator can place the load precisely. Always check the delivery is MOT Type 1 spec, not generic "hardcore".