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 takes your length and width, or a total area you already know, multiplies by the compacted depth for the volume, adds a wastage buffer, and applies a standard sub-base density to estimate the tonnes (and bulk bags) to order. A compaction allowance then converts the finished volume into the larger loose volume delivered. It is also the sub-base tool for a tarmac drive: enter the drive's area at 150mm, then size the surface on top with the tarmac quantity calculator. The wider general calculators hub has the rest of the everyday tools.
The formula
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. The compaction allowance changes the loose volume only, not the tonnes.
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%
- Compaction allowance:
- 20%
- 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
- Loose volume: 3.0 m³ ÷ (1 − 0.20) = 3.75 m³
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.
MOT Type 1 sub-base needed by compacted depth
| 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.
Published density and compaction figures
| Figure | Value | Where it comes from |
|---|---|---|
| MOT Type 1, compacted density | 2.15 t/m³ | civils.ai aggregate calculator |
| Crushed concrete, compacted density | 2.00 t/m³ | civils.ai aggregate calculator |
| Loose to compacted volume factor | × 1.3 (a drop in level of about 23%) | Marshalls sub-base guide; the 23% is our arithmetic (1 − 1 ÷ 1.3) |
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. Under tarmac the sub-base is the hidden engine of the drive: the surface is a flexible wearing course, and the weight of a parked car is carried almost entirely by the compacted stone beneath it. Size the surface with the tarmac quantity calculator and budget the whole build with the tarmac driveway cost calculator.
Tips and common pitfalls
- Order for the compacted depth. Loose stone settles as it is rolled, so allow for wastage in the tonnes and for compaction in the loose volume you book.
- 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.
- Never substitute clean gravel. Without fines it will not bind, and a tarmac surface laid over it will fail.
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 much MOT Type 1 do I need for my project?
Multiply the area by the compacted depth for the volume in cubic metres, then 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. If you already know the area, such as a 40 m² drive, use the Total area option. Add 5–10% for wastage 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.
How much extra MOT Type 1 should I order for wastage and compaction?
Add 5% to 10% to the tonnes for site variation and spillage, so a short load does not halt the job. Compaction is separate: rolling drives the air out and the level drops, so the loose volume delivered is larger than the finished volume. Marshalls multiplies by 1.3, a drop of about 23%, and the calculator offers 15%, 20% and 25%.
Can I use gravel or shingle instead of MOT Type 1?
No. Clean gravel and shingle have no fines to bind them, so the stones roll against each other and never compact into a solid base. MOT Type 1 is graded from 40mm stone down to dust, and the dust is what locks the layer together under a roller or plate.
Is MOT Type 1 the sub-base to use under a tarmac driveway?
Yes. MOT Type 1 is the standard structural sub-base beneath tarmac as well as block paving and slabs, and about 150mm compacted is typical for a domestic drive. Enter the drive's area here for the sub-base, then size the tarmac on top with the tarmac quantity calculator.
Related paving calculators
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. The compaction allowance is a planning figure, not a measured one.
- 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.