MOT Type 1 calculator: tonnes and bulk bags
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
MOT Type 1 is ordered by weight. At our default density (2.1 t/m³ compacted, a typical figure), each square metre at 100 mm finished depth needs 0.21 t, so 5 × 4 m at 100 mm is 4.2 t: five 0.85 t bulk bags. Enter the compacted depth, or switch to loose if you only know the depth as spread.
Work out tonnes and bulk bags of MOT Type 1 or recycled Type 1 below; every figure we start from is shown and you can change it. "Type 1" means the Specification for Highway Works clause 803 grading.
Worked example
| You enter | Value |
|---|---|
| Area | rectangle 5 m × 4 m |
| Depth | 100 mm |
| The depth above is | Compacted (finished) |
| Material | MOT Type 1 (compacted) |
| Density | 2.1 t/m³ |
| Waste allowance | 0% |
| Bulk bag size | 0.85 t |
| Small bag size | 25 kg |
Order: 5 bulk bags
| Result | Value |
|---|---|
| Bulk bags | 5 |
| Small bags | 168 |
| Weight | 4.2 t |
| Compacted volume (with waste) | 2 m³ |
| Area | 20 m² |
Show the working
- Area: Area 1 20 m² = 20 m²
- Volume: 20 m² × 0.1 m = 2 m³
- With 0% waste: 2 × 1 = 2 m³
- Weight: 2 m³ × 2.1 t/m³ = 4.2 t
- Bulk bags: 4.2 t ÷ 0.85 t = 4.94, rounded up to 5
- Small bags: 4,200 kg ÷ 25 kg = 168, rounded up to 168
How it works
- Volume (m³) = area (m²) × depth (m) × (1 + waste)
- Loose depth: compacted volume = loose volume ÷ compaction factor; loose volume = compacted volume × compaction factor
- Weight (t) = volume (m³) × density (t/m³)
- Bulk bags = weight (t) ÷ bulk bag size (t), rounded up
- Small bags = weight (t) × 1,000 ÷ small bag size (kg), rounded up
Enter the depth your design or installer specifies. We don't recommend a depth.
The densities are for compacted material, so the tonnes are what you order whichever depth you enter. If you measure a loose depth (as spread, before the roller or plate), we turn it into a compacted volume with your supplier's compaction factor.
Recycled Type 1 is made from crushed concrete and masonry. Its density differs from quarried Type 1, so the tonnes differ: use your supplier's figure.
Compaction varies, so order by weight and check with your supplier.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Compaction factor: loose volume ÷ compacted volume | Enter from the bag, pack or tin | Typical value Not yet checked against the source | From your product brief v2 §2 (sub-base: compacted vs loose toggle). Loose volume ÷ compacted volume for MOT Type 1. Researcher to source from an aggregate supplier or laying guide (e.g. Brett, Tarmac, Marshalls); until then the user enters their supplier's figure. |
| Density: MOT Type 1 (compacted) | 2.1 t/m3 Sources range 2–2.2 t/m3 | Typical value Not yet checked against the source | agg.directory calculator (worked 4.2 t example) (checked 19 October 2026) Compacted. Supplier's figure takes precedence. |
| Density: Recycled Type 1 (compacted) | 1.9 t/m3 | Typical value Not yet checked against the source | aggregatecalculator.co.uk aggregate density table (checked 19 October 2026) Compacted. |
| Waste allowance | 5 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job Compaction varies. |
| Bulk bag size | 0.85 t | Common UK size Not yet checked against the source | builder.tools bulk bag figure (checked 19 October 2026) Varies by merchant; check yours. |
| Small bag size | 25 kg | Common UK size Not yet checked against the source | From your product Common small bag. |
Regulations and standards
- Specification for Highway Works, Series 800, Clause 803 (Type 1 unbound mixtures): what suppliers mean by "Type 1"
Explained: SHW clause 803 (Type 1 sub-base).
Our checks use the guidance for England unless a badge says otherwise. Wales, Scotland and Northern Ireland have their own rules: check the source for where you live.
FAQs
How much MOT Type 1 do I need?
Multiply the area (m²) by the finished, compacted depth (m) to get the volume, then by the density (t/m³) to get tonnes, and add a waste allowance. The calculator does this for you and shows each step. With our defaults, 20 m² at 100 mm is 2 m³ and 4.2 t before waste.
How many bulk bags of Type 1 do I need?
Divide the tonnes by the bag size and round up. Our default bulk bag is 0.85 t because bag sizes vary between merchants, so check yours and change the figure under More settings. The calculator also gives the number of 25 kg small bags for small jobs.
What's the difference between compacted and loose depth?
Type 1 is spread loose and then compacted with a plate compactor or roller, so it ends up thinner than it was spread. Most laying guides give the finished (compacted) depth, which is what the calculator expects by default. If you only know the loose depth, choose "Loose" and enter the compaction factor from your supplier: loose volume divided by compacted volume.
Is recycled Type 1 the same weight as MOT Type 1?
Not quite. Recycled Type 1 is made from crushed concrete, brick and similar materials, and it is usually lighter per cubic metre, so the same volume weighs less. Our default for recycled Type 1 is 1.9 t/m³, against 2.1 t/m³ for primary Type 1, giving 3.8 t instead of 4.2 t for the same 20 m² at 100 mm. Use your supplier's figure if they give one.
How deep should a sub-base be?
It depends on the job, the ground and what goes on top, so this page doesn't set a depth. Use the depth in the laying guide for your slabs or blocks, or ask your builder, especially for a drive that cars will use. The patio and block paving calculators follow on from this one.
Is Type 1 the same as hardcore?
"Hardcore" is a loose term for any broken rubble or stone used as fill. MOT Type 1 is a specified material: a graded crushed aggregate that meets the clause 803 grading, which is why it compacts into a firm, even layer. Ask for Type 1 by name if a laying guide specifies it.
Guides
MOT Type 1 sub-base explained
What MOT Type 1 is, why it's compacted, and how to order it by weight for a patio, path or drive.
Patio base materials list
The layers under a patio and how to work out sub-base, bedding sand or mortar and paving quantities for your area.