MOT Type 1 Calculator
Calculate compacted sub-base volume and estimate tonnes from the area, finished depth, supplier density and your chosen ordering allowance.
Calculate MOT Type 1 quantity
How to calculate MOT Type 1 sub-base
Start with the finished geometry. Multiply the surface area by the required compacted depth, expressed in metres. That gives the compacted layer volume in cubic metres. If you want an ordering margin, apply it to that volume. Convert the resulting volume to tonnes only after choosing a density appropriate to the actual aggregate being supplied.
Estimated tonnes = compacted volume × (1 + allowance ÷ 100) × supplier density (t/m³).
Base the calculation on the area and compacted construction depth shown for the job.
Use an explicit percentage only where you want extra ordering tolerance for real site variation.
Density is editable because tonnes per cubic metre is a product conversion, not a universal constant.
Worked example: 40 m² at 150 mm
40 m² × 0.15 m = 6.00 m³ of compacted sub-base.
With a 10% ordering allowance, the order volume becomes 6.60 m³. Using the calculator's editable example density of 2.00 t/m³ gives an estimated 13.20 tonnes.
The 2.00 t/m³ figure is an example input, not a claim that every Type 1 product has that density.
What “MOT Type 1” means
UK government driveway guidance describes Type 1 sub-base as a graded gravel containing a range of stone sizes, including fine material that fills the voids between larger particles. In highway specifications, products sold as Type 1 are commonly tied to the relevant granular sub-base specification, so the material description on a quote or delivery ticket matters.
For domestic estimating, use the product your supplier is actually selling and its declared conversion data. For specified or adoptable highway work, follow the project specification and approved material requirements rather than treating “MOT Type 1” as a generic substitute. Sources: GOV.UK driveway guidance and Salford City Council approved Type 1 materials.
Compacted depth is not the same as loose delivered volume
This calculator asks for the finished compacted depth. Aggregate delivered loose, tipped or stockpiled is not automatically the same volume as the finished compacted layer. Rather than hiding that difference inside an unexplained rule of thumb, the tool calculates the compacted geometry first and then lets you add an explicit ordering allowance.
- Do not enter a loose depth if the drawing or specification gives a finished compacted depth.
- Do not use the allowance percentage as a structural design rule. It only increases the quantity being estimated.
- Do not assume every supplier converts m³ to tonnes identically. Replace the example density with product-specific information where possible.
- Round to the supplier's real delivery unit. Bulk loads, tonne bags and loose loads may be sold differently.
Type 1 and permeable construction
Do not assume conventional Type 1 is suitable where the construction relies on a permeable sub-base. GOV.UK guidance notes that the fines in Type 1 make it relatively difficult for water to pass through quickly and separately describes open-graded sub-base materials used for drainage. Follow the drainage design and specified aggregate for the project.
Planning estimate only. This calculator does not select the correct sub-base material, construction depth, pavement build-up or drainage design. Check drawings, ground conditions, loading, specification and supplier information before ordering or laying material.
Continue the groundworks workflow
Frequently asked questions
How do I calculate how much MOT Type 1 I need?
Multiply the area in square metres by the compacted depth in metres to get the compacted layer volume in cubic metres. Add any chosen ordering allowance, then multiply by a suitable supplier bulk-density figure if you need an estimated weight in tonnes.
What density should I use for MOT Type 1?
Use the density or tonnes-per-cubic-metre conversion supplied for the actual product where possible. The calculator keeps density editable because aggregate source, grading and moisture can affect the conversion.
Does the calculator include compaction?
Enter the finished compacted layer depth required by the drawing or specification. The separate percentage field is an ordering allowance for quantity variation, not a design rule for compaction.
Can I use MOT Type 1 for a permeable driveway?
Do not assume so. UK government guidance notes that Type 1 contains fine material and is relatively slow to drain, while open-graded alternatives may be used where permeability is required. Follow the project drainage design and product specification.
Is MOT Type 1 the same as hardcore?
No. UK government guidance describes Type 1 as a better-quality graded sub-base material containing a range of stone sizes and fines. Confirm the specified product rather than substituting generic hardcore.
Does this tool tell me the correct sub-base depth?
No. It calculates quantity from the compacted depth you enter. Required depth depends on the pavement or project design, ground conditions, loading and specification.