How this calculator works
The amount of aggregate you need depends on the length, width and depth of the area, and turning that volume into a weight requires the density of MOT Type 1. This tool does both: it multiplies your dimensions for the volume, adds a wastage buffer, and applies a standard sub-base density to estimate the tonnes (and bulk bags) to order. If you are building specifically under a tarmac surface, the tarmac sub-base calculator uses the same method with a compaction allowance, and the wider general calculators hub has the rest of the everyday tools.
The formula
Volume (m³) = Length × Width × Depth
Volume with wastage = Volume × (1 + wastage %)
Tonnes required = Volume with wastage × Density
Keep units consistent — convert a depth in millimetres to metres (÷ 1000) before multiplying. The calculator defaults to a density of about 2.0 t/m³; the practical range for MOT Type 1 is roughly 2.0–2.2 t/m³ depending on the stone and its moisture content.
Worked example
Example — a 20 m² area at 150 mm compacted
- Area:
- 5 m × 4 m = 20 m²
- Depth:
- 150 mm = 0.15 m
- Density:
- 2.0 t/m³ (default)
- Wastage:
- 10%
- Volume: 20 m² × 0.15 m = 3.0 m³
- Tonnage: 3.0 m³ × 2.0 t/m³ = 6.0 t
- With wastage: 6.0 t × 1.10 = 6.6 t
MOT Type 1 to order: ≈ 6.6 tonnes
At the top of the density range (2.2 t/m³) the same area would need about 7.3 tonnes, so confirm the supplier's figure for a precise order.
Reference data
| Compacted depth | Volume per m² | Tonnes per m² (≈2.0–2.2 t/m³) |
|---|---|---|
| 75 mm (path) | 0.075 m³ | 0.15–0.17 t |
| 100 mm (patio / shed base) | 0.100 m³ | 0.20–0.22 t |
| 150 mm (driveway) | 0.150 m³ | 0.30–0.33 t |
| 200 mm (heavy use / soft ground) | 0.200 m³ | 0.40–0.44 t |
The depth-to-use mapping above is common practice rather than a fixed standard: heavy vehicles or exceptionally weak ground can need more depth. Where the ground is soft, lay a woven geotextile membrane first and compact the stone in layers of up to 75mm.
Key facts
- MOT Type 1 is a compactable granular sub-base, historically approved by the Ministry of Transport, usually crushed limestone or granite from 40mm down to dust.
- MOT Type 1 is commonly estimated at 2.0–2.1 tonnes per cubic metre as supplied, so 1 m³ at 150mm depth covers about 6.7 m².
- A domestic driveway typically uses 150mm of compacted MOT Type 1; paths use about 75mm and patios about 100mm.
- Adding 5–10% wastage to an MOT Type 1 order covers compaction settlement, site variation and spillage during spreading.
Who should use this and when
This is for anyone laying a hard surface who needs to order aggregate before the groundworks start — a driveway, a patio, a path or a shed base. Getting the quantity right avoids two common problems: ordering short and stopping a compaction run, or ordering long and paying to remove surplus stone. It matters most on soft ground, where under-specifying the sub-base depth is the usual cause of a surface that later cracks or ruts. For a tarmac drive specifically, pair it with the tarmac quantity calculator to size the surface course above.
Tips and common pitfalls
- Order for the compacted depth. Loose stone settles as it is rolled, so a wastage or compaction allowance is essential.
- Compact in thin layers. Up to 75mm per lift, or the bottom of a deep layer never reaches full density.
- Match density to the stone. Recycled crushed concrete is lighter than primary limestone or granite; confirm the figure with your supplier.
- Don't skimp on depth over soft ground. Weak subsoil needs more sub-base and often a membrane to stay stable.
Frequently asked questions
What is MOT Type 1 used for?+
MOT Type 1 is a compactable granular sub-base laid under driveways, patios, paths, roads and shed bases. Once compacted, it forms a stable, frost-resistant, load-bearing layer that spreads the weight above it so the surface — tarmac, paving or slabs — does not sink.
How deep should MOT Type 1 be for a driveway?+
A domestic driveway typically uses about 150mm of compacted MOT Type 1. Paths need around 75mm and patios or shed bases about 100mm. Heavier vehicles or soft ground call for more depth — 200mm or above — to keep the base stable.
How do I calculate MOT Type 1 tonnage?+
Multiply length by width by depth for the volume in cubic metres, then multiply by the density — about 2.0 to 2.1 tonnes per cubic metre. For example, 20 m² at 150mm is 20 × 0.15 × 2.0 = 6 tonnes. Add 5–10% for wastage and settlement before ordering.
How many tonnes of MOT Type 1 are in a cubic metre?+
Roughly 2.0 to 2.1 tonnes per cubic metre as commonly supplied, rising toward 2.2 once fully compacted with heavier crushed rock. The exact figure depends on the stone type, grading and moisture content, so treat it as an estimate rather than a fixed constant.
Should I add extra for wastage?+
Yes. Adding 5% to 10% covers site variation, compaction settlement and spillage during spreading, and reduces the risk of under-ordering. It is cheaper to have a little spare than to halt a job waiting on a second delivery.
Is MOT Type 1 the same as the tarmac sub-base?+
Yes — MOT Type 1 is the standard structural sub-base beneath tarmac as well as block paving and slabs. If you are specifically building under a tarmac drive, the tarmac sub-base calculator applies the same method with tarmac-focused defaults.
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Estimates & assumptions
- Volume is exact (length × width × depth); tonnage uses an estimating density of about 2.0–2.2 t/m³, which varies with the stone and its moisture content.
- Typical depths (150mm driveway, 100mm patio, 75mm path) are common practice, not a substitute for a ground assessment on difficult sites.
- The tool does not perform geotechnical design or account for membranes, drainage or edge restraints.
- Confirm the exact density and bag weight with your aggregate supplier for a precise order.
Estimates are for material planning. On soft or made-up ground, seek professional advice on the required sub-base depth.