MOT Type 1 Calculator

By Gary Hodson · Ex-Army. I do the sums so you buy the right amount. · Depths, grading and compaction checked against Marshalls and Tarmac technical guides · Last reviewed 8 October 2026

This free sub-base calculator works out exactly how much MOT Type 1, crusher run, scalpings or sharp sand you need for any foundation project. Enter your area in metres or feet, set the depth in millimetres or inches, choose your material, and get an instant answer in cubic metres, tonnes, bulk bags and 25kg bags.

The calculator uses the formula length × width × depth to find the volume, then multiplies by the density of your chosen material. MOT Type 1 is the heaviest at 2,100 kg/m³, while sharp sand is lighter at 1,600 kg/m³. Getting the density right is important because sub-base materials are sold by weight in the UK.

This calculator also works as a hardcore calculator: select “Hardcore / Recycled aggregate” from the material dropdown to get quantities for bulk fill and backfilling projects.

This calculator also works as a general aggregate calculator: pick the closest material from the dropdown to estimate tonnage for sand, ballast, scalpings or recycled aggregate.

Need to calculate the surface layer too? Our gravel calculator works out decorative stone quantities, the paving calculator handles slab counts for patios, and the concrete calculator covers shed bases and fence post foundations. Not sure which stone to ask for? Read what MOT Type 1 is and how it differs from hardcore and Type 3. If a deck is going on top of the base, our composite vs timber decking guide compares the board materials.

The right depth depends on the ground conditions and what the surface will support. These are Pavingexpert’s duty classes, with Marshalls’ block paving minimum. For a gravel surface on top, see our guide to how deep gravel should be.¹⁴

Different sub-base materials have different properties. Here's how they compare.

A properly laid sub-base is the foundation of any hard landscaping project. Getting this right prevents sinking, cracking and drainage problems later.

1. Excavate to the right depth

Dig out the area to your required depth plus the thickness of the surface layer (paving slabs, gravel, etc.). Allow for the sub-base, bedding layer and surface material. For a patio with 50mm paving on 30mm sand bedding over 100mm sub-base, you need to excavate 180mm total.³

2. Compact the subgrade

Before adding any material, compact the bare ground with a plate compactor or roller. This prevents settlement. If the ground is soft clay, consider laying geotextile membrane on top to stop the sub-base mixing into the clay.⁵

3. Lay and compact the sub-base

Add MOT Type 1 or crusher run in layers. Marshalls says no layer should be thicker than 75mm (3 inches).³ Pavingexpert allows up to 150mm a layer.¹ Compact each layer with a plate compactor before adding the next. For a 150mm sub-base, two 75mm layers keep you inside both figures. The finished surface should be level and firm enough to walk on without leaving footprints.

The area that one tonne of MOT Type 1 covers depends on the depth you lay it. Use this quick reference table to estimate quantities without a calculator.

These figures apply 2,100 kg/m³ to the compacted depth you enter, so they already allow for the extra loose material that squashes down when you compact it. Pavingexpert’s 5 m² per tonne at 100mm compacted works out at about 2,000 kg/m³. Order a little extra for uneven ground, and check with your supplier.

“Hardcore” and “MOT Type 1” are often used interchangeably, but they’re not the same thing. Understanding the difference helps you choose the right material and avoid overspending.

What is hardcore?

Hardcore is a loose trade name for broken or crushed material used as fill, such as broken brick or concrete. It has no set grading, so it varies from load to load. You might see it called “clean hardcore” or “recycled aggregate”.

When to use hardcore

Hardcore is fine for backfilling trenches, raising levels, or as a bulk fill layer under a proper sub-base. It’s not recommended as the final sub-base layer under paving or driveways because the irregular sizing makes it difficult to compact to a flat, stable surface.

When to use MOT Type 1

MOT Type 1 is the industry standard sub-base for any hard landscaping project: driveways, patios, paths and shed bases. Its mix of particle sizes, from dust up to a top size of typically 40mm (Clause 803 allows up to 63mm), interlocks when compacted, creating a solid, load-bearing foundation. If you’re laying paving slabs, block paving or gravel on top, always use MOT Type 1 for the final sub-base layer.⁶

Pro tip: For budget-conscious projects, lay hardcore as bulk fill, then finish with MOT Type 1 on top at the depth your project needs.

Planning to lay tarmac on top of your sub-base? Use our tarmac calculator to work out how much tarmac or asphalt you need for your driveway, path or car park.

To calculate how much hardcore you need, the process is identical to calculating MOT Type 1: multiply length × width × depth (all in metres) to get the volume in cubic metres, then multiply by the density. Hardcore is slightly lighter than MOT Type 1 at roughly 1,900–2,000 kg/m³ because it has more voids between particles.

Hardcore Worked Example

Suppose you need to backfill a 4m × 3m area to a depth of 200mm (0.2m) with hardcore before laying MOT Type 1 on top:

• Volume: 4 × 3 × 0.2 = 2.4 cubic metres
• Weight: 2.4 × 1,950 = 4,680 kg = 4.68 tonnes
• Bulk bags (850kg): 4,680 ÷ 850 = 6 bulk bags

Use the calculator at the top of this page to run the numbers for your project. Simply enter your area and depth, and the results work for hardcore, MOT Type 1, crusher run or any aggregate with a similar density. For hardcore, pick it in the material dropdown: the calculator uses 2,000kg per cubic metre for hardcore and 2,100kg for MOT Type 1.

Prices vary by region and supplier, but here are typical UK costs for MOT Type 1 sub-base as of 2026.

For quantities over 5 tonnes, get quotes from local aggregate suppliers.

Choosing the right sub-base aggregate is one of the most important decisions in any groundwork project. Each material has different particle sizes, compaction characteristics and drainage properties. Use the wrong type and a patio or driveway can fail, so here is a proper breakdown of the five main sub-base aggregates you will encounter in the UK.

MOT Type 1 (Graded Crushed Aggregate)

MOT Type 1 is the gold standard for sub-base work in the UK. It is a graded, angular aggregate made from crushed rock, crushed slag or recycled aggregate, and it must meet Clause 803 of the Specification for Highway Works. Tarmac’s is generally 40mm down to dust. Clause 803 allows particles up to 63mm, with most under 31.5mm, so the top size varies by product. The mix of sizes is deliberate: the fines fill the gaps between the larger stones, creating an interlocking matrix that compacts into an extremely dense, stable layer. For most domestic projects (driveways, patios, shed bases, paths), MOT Type 1 is the correct choice.⁶²

MOT Type 3 (Open-Graded, Free-Draining)

MOT Type 3 is a crushed, open-graded aggregate of about 40mm down to dust, made to Clause 805 of the Specification for Highway Works. It has a low fines content, not zero fines, so water drains through it freely while it still carries load. It is the sub-base usually specified for permeable paving. For ordinary paving that sheds water, Type 1 is the usual choice. If you are laying permeable paving, follow the build-up the paving maker gives.²

Recycled Aggregate (6F2)

MOT Type 1 itself can be made from recycled aggregate, as long as it meets Clause 803 of the Specification for Highway Works.⁶ So if you want a recycled sub-base, ask for Type 1 to Clause 803. If you are offered material sold as 6F2 instead, ask the supplier for its grading and test results, and whether it suits your job as the main sub-base or only as fill under the Type 1.

Scalpings

Scalpings is a quarry term for small offcuts, chippings or crushed stone. Sold as 40mm scalpings, it runs from about 40mm down to dust, a similar size range to Type 1, but with no control over the grading. A load can be heavy on lumps or heavy on fines, and it often has more fines than Type 1, so it will not carry load as well as a true Type 1.²

Crusher Run

Crusher run is rock put through a crusher and then screened to take out anything bigger than a set size, usually 50mm. Like scalpings, it has no proper grading and tends to have more fines, so it carries load less well than Type 1. Pavingexpert gives 50mm of compacted crusher run as an alternative to Type 1 for foot-traffic paths and patios, and for light domestic drives. Larger sizes, such as 75mm and 100mm crusher run, are too chunky for a sub-base and are used as fill.²¹

If you are unsure which aggregate to use, MOT Type 1 is the safe default for any load-bearing project. Where the sub-base must drain freely, such as under permeable paving, use Type 3. Crusher run suits paths, patios and light domestic drives, and scalpings suit light jobs, because neither has a set grading. If you want a recycled option, ask for Type 1 made to Clause 803, and check with your supplier before using anything sold as 6F2 as the main sub-base under a driveway.

A properly laid sub-base is the single most important factor in the longevity of any patio, driveway or path. Poor sub-base work is what makes patios sink. Here is the process, step by step.

Step 1: Mark Out and Excavate

Mark out your area using string lines and pegs. Excavate to the total depth you need. This includes the sub-base, any bedding layer, and the surface material. For a typical patio with 50mm paving slabs on a 30mm sand bed over 100mm of sub-base, you need to dig out 180mm below your finished surface level. For a driveway with block paving (50mm) on 30mm sand over 150mm sub-base, excavate 230mm. Check your levels regularly with a spirit level and straight edge.³⁴

Step 2: Lay Geotextile Membrane on Soft Ground

If your subsoil is clay, silt, or anything soft enough to leave a footprint when you stand on it, lay a geotextile membrane across the entire excavated area. The membrane acts as a separation layer, preventing the sub-base aggregate from being pushed down into the soft subsoil by traffic and weather. Without it, your carefully compacted sub-base will gradually sink into clay soil over a few years, taking your paving with it. On firm, well-drained ground (gravel, chalk, sandy subsoil), you can skip this step.

Step 3: Spread Sub-Base in Thin Layers

This is where most DIYers go wrong. Do not dump the full depth of sub-base in one go and compact the top. A plate compactor (also called a wacker plate) needs the material in layers. Marshalls caps each layer at 75mm.³ Pavingexpert's ceiling is 150mm, and anything deeper must be built up in layers.¹ Rake each layer roughly level, compact it, then add the next. For a 150mm sub-base, that is two 75mm layers. It takes longer, but it is how the base stays put.

Step 4: Compact Each Layer Thoroughly

Hire a plate compactor and run it across each layer in overlapping passes, working from the edges inward. The surface should feel solid underfoot. If you can leave a footprint in the compacted sub-base, it needs more work. For small areas like a single shed base, a hand tamper will do the job, though it requires considerably more effort.

Step 5: Check Levels and Drainage Falls

Once your final layer is compacted, check the surface is level using a long spirit level or a straight timber edge. The sub-base should fall very slightly away from any buildings. A gradient of 1:80 (roughly 12mm per metre) is standard. This ensures rainwater drains away from your house. If any areas are high or low, add or remove material and re-compact. Getting this right now saves you from relaying paving later. Once the sub-base is level, firm and draining correctly, you are ready for your bedding layer and surface material. Our paving calculator can help you work out how many slabs you need, or use the concrete calculator for a slab base.³ For the mix to use on that slab base, see our concrete mix ratios guide.

Why Compaction in Layers Matters

Compaction in layers is not optional. It is the difference between a patio that stays level and one that sinks. When you compact a thin layer of MOT Type 1, the vibration forces the fine particles into the gaps between the larger stones, creating a dense, interlocked matrix. Pile on more than one layer's worth and compact only the top, and the lower material can stay loosely packed. Over time, traffic and the freeze-thaw cycle will cause the loose material to settle, creating dips, cracks and uneven surfaces above. Professionals always compact in layers, and there is a good reason for it.

Understanding the true cost of sub-base material helps you budget accurately and avoid nasty surprises. The price per tonne varies dramatically depending on how you buy it. Here is a breakdown of real-world UK prices as of early 2026.

Price by Purchase Format

Sub-base comes in 25kg bags from DIY shops such as B&Q or Wickes, in bulk bags, or loose by the tonne. At £5–£7 per bag, you are paying £200–£280 per tonne. Bulk bags (850kg) cost £50–£70 each, bringing the per-tonne price down to around £60–£82. Loose delivery from a local aggregate supplier or quarry is £35–£55 per tonne, plus delivery.

Project Cost Estimates

To give you a practical idea of what sub-base costs for real projects, here are worked examples using MOT Type 1 at mid-range pricing (£45 per tonne loose delivery, plus £50 delivery charge). These include only the sub-base material, so add your surface material, bedding sand, and any hire costs on top.

These tonnages are the plain volume with no extra added. Order a little extra and check with your supplier. If you want to cut costs, ask your supplier for recycled MOT Type 1, or a recycled fill for the lower layers, and compare the price per tonne with virgin Type 1. Keep material that meets Type 1 for the top, load-bearing layer. You can also collect material yourself from a local quarry or builders’ merchant to avoid the delivery charge, provided you have a suitable vehicle or trailer.

These are the common sub-base mistakes. Every single one of these leads to a failed surface: sunken paving, cracked concrete, pooling water. Here is what to watch out for.

1. Not Going Deep Enough

Pavingexpert puts a light-to-medium domestic drive at 100mm of compacted Type 1. For medium duty, such as vans and small pick-ups, it gives 150mm.¹ Marshalls recommends at least 150mm under block paving for most domestic jobs. It is tempting to lay only 75mm under a driveway because “it is only a car.” A car’s whole weight sits on four small tyre contact patches. On too thin a sub-base, the aggregate shifts under repeated loading, and within a year or two you get ruts and dips. For patios and paths, Pavingexpert gives 75mm for foot traffic only. For a driveway, Marshalls’ 150mm minimum is the safer choice, and Marshalls says the design must be based on the ground conditions and the loads.⁴

2. Compacting the Full Depth in One Pass

This is covered in the laying guide above, but it bears repeating. If you tip in the full depth and compact only the top, the lower material can stay loose. It settles slowly over weeks and months, taking your paving with it. Keep each layer to 75mm, as Marshalls advises.³ Never go over 150mm, which is Pavingexpert's limit.¹ It takes longer, but it gives you a solid base.

3. Using MOT Type 3 Where Type 1 Is Needed

Type 3 is made to drain. It is open-graded with a low fines content, so water passes through it. It is the sub-base usually specified for permeable paving, where the paving maker sets the build-up. Under ordinary block paving, slabs or tarmac that shed water, use Type 1, which compacts into a denser layer.²

4. Skipping Geotextile Membrane on Clay Soil

Clay soil is the enemy of sub-bases. It is soft, it holds water, and it expands and contracts with the seasons. If you lay MOT Type 1 directly onto clay, the aggregate slowly gets pushed down into the clay by traffic and vibration. Over a few years, you lose depth and stability. A geotextile membrane between the clay and the sub-base prevents the aggregate mixing with the subsoil. On sandy or gravelly subsoil, you do not need it. On clay, you absolutely do.⁵

5. Ignoring Drainage

If water cannot drain away from under your paving, it saturates the sub-base and softens the subsoil beneath. In winter, trapped water freezes and expands, heaving the surface upward. When it thaws, the surface drops back, but not evenly, leaving you with cracks and dips. Always ensure your sub-base has a slight fall (1:80 gradient, about 12mm per metre) directing water away from buildings and toward a drain, soakaway or garden. If your site has naturally poor drainage, consider laying a land drain around the perimeter before you start the sub-base. Our gravel calculator can help you plan a gravel drainage border around the finished surface.³