Overview
The sub-base is the load-spreading layer, so its depth is a design decision — the calculator quantifies whatever depth you specify.
How the calculation works
Sub-base tonnage = area × compacted depth × planning density. Type 1 and limestone scalpings plan around 2.0-2.2 t/m³; recycled options around 1.8-2.2 t/m³.
Because a sub-base is compacted in thin passes, ordering needs loose volume: the compaction allowance converts compacted tonnes into the loose quantity to buy.
Bedding and surface layers above the sub-base (sharp sand, gravel) are separate quantities — calculate each layer individually.
Worked example
A patio 5m × 4m specifies a 100mm compacted MOT Type 1 sub-base.
Area = 20 m². Volume = 2.0 m³. Weight = 2.0 × 2.2 = 4.4 tonnes.
Ordering with 10% allowance gives 4.84 tonnes — six 850kg bulk bags, or a 5-tonne loose load where available.
MOT Type 1 at a glance
- Planning density2.20 t/m³
- Typical range2.00–2.30 t/m³
- CategorySub Base
- CompactionOften relevant
- SourcePlanning midpoint of published UK supplier data (≈2.0–2.3 t/m³ range observed)
- Reviewed2026-08-16
Planning values for typical UK supplies; your supplier product data takes precedence.
MOT Type 1 coverage guide
| Depth | Area per tonne | Area per 850kg bag | Weight per m² |
|---|---|---|---|
| 25mm | 18.2 m² | 15.5 m² | 55 kg |
| 40mm | 11.4 m² | 9.7 m² | 88 kg |
| 50mm | 9.1 m² | 7.7 m² | 110 kg |
| 75mm | 6.1 m² | 5.2 m² | 165 kg |
| 100mm | 4.5 m² | 3.9 m² | 220 kg |
| 150mm | 3.0 m² | 2.6 m² | 330 kg |
Computed from a 2.20 t/m³ planning density on level ground.
Assumptions and accuracy
Depths entered should be compacted finished depths; loose-laid material thickens the layer until compacted.
Planning densities vary with grading and moisture; supplier data takes precedence.
For load-bearing or highway situations, check the specification required for your project and confirm quantities with your contractor or material supplier.
Planning density values
Use supplier product data whenever available. These figures are planning defaults shared by every calculator on the site.
| Material | Category | Planning density | Typical range | Compaction |
|---|---|---|---|---|
| MOT Type 1 | Sub Base | 2.20 t/m³ | 2.00–2.30 t/m³ | Relevant |
| MOT Type 3 | Sub Base | 2.10 t/m³ | 1.90–2.20 t/m³ | Relevant |
| Recycled Type 1 | Recycled | 2.00 t/m³ | 1.80–2.20 t/m³ | Relevant |
| 6F2 / 6F5 crushed aggregate | Recycled | 2.00 t/m³ | 1.80–2.20 t/m³ | Relevant |
| Road planings | Recycled | 2.00 t/m³ | 1.80–2.20 t/m³ | Relevant |
| Sharp sand | Sand | 1.60 t/m³ | 1.50–1.70 t/m³ | Usually no |
| Building sand | Sand | 1.50 t/m³ | 1.40–1.60 t/m³ | Usually no |
| Kiln-dried sand | Sand | 1.50 t/m³ | 1.40–1.60 t/m³ | Usually no |
| 10mm pea shingle | Gravel | 1.60 t/m³ | 1.40–1.70 t/m³ | Usually no |
| 20mm gravel / shingle | Gravel | 1.60 t/m³ | 1.40–1.70 t/m³ | Usually no |
| Decorative gravel | Decorative | 1.50 t/m³ | 1.30–1.70 t/m³ | Usually no |
| Slate chippings | Decorative | 1.60 t/m³ | 1.40–1.80 t/m³ | Usually no |
| Gabion stone | Gravel | 1.50 t/m³ | 1.40–1.60 t/m³ | Usually no |
| Self-binding gravel | Gravel | 1.90 t/m³ | 1.80–2.10 t/m³ | Relevant |
| Crushed concrete | Recycled | 1.90 t/m³ | 1.70–2.10 t/m³ | Relevant |
| Limestone scalpings | Sub Base | 2.00 t/m³ | 1.80–2.20 t/m³ | Relevant |
| Ballast | Sand | 1.70 t/m³ | 1.60–1.80 t/m³ | Usually no |
| Generic aggregate | General | 1.70 t/m³ | 1.50–2.20 t/m³ | Usually no |
Typical depth guidance by project type
| Project type | Common depth range | Typical materials |
|---|---|---|
| Driveway | 100–150mm compacted | MOT Type 1, Recycled Type 1, 6F2 / 6F5 crushed aggregate |
| Garden path | 50–100mm compacted | 20mm gravel / shingle, Self-binding gravel, Decorative gravel |
| Patio sub-base | 75–100mm compacted | MOT Type 1, Recycled Type 1, Sharp sand |
| Decorative border | 40–50mm compacted | Decorative gravel, Slate chippings, 10mm pea shingle |
| Shed base | 75–100mm compacted | MOT Type 1, Limestone scalpings, Ballast |
| Drainage layer | 50–150mm compacted | 10mm pea shingle, 20mm gravel / shingle |
| General fill | 100–300mm compacted | 6F2 / 6F5 crushed aggregate, Crushed concrete, Generic aggregate |
Common planning ranges only; ground conditions and loads can require a different specification.
How to use this calculator
- Measure the full area including edges that will be cut and compacted.
- Enter the specified compacted sub-base depth.
- Select the specified material — the planning density updates automatically.
- Calculate each construction layer separately and add the results for a total order.
When sub-base is commonly used
Sub-bases carry pavements, patios, driveways and sheds. Type 1 is the standard specified option; Type 3 drains freely under permeable paving; 6F2 and crushed concrete suit capping and fill beneath.
Frequently asked questions
How much sub-base do I need?
For each 100mm of compacted sub-base allow 0.1 m³ per square metre — roughly 200-220kg of Type 1 per m². Multiply by your area and add an ordering allowance.
Do I calculate sub-base loose or compacted?
Enter the compacted finished depth and add a compaction allowance (commonly 10-20%) when ordering loose material, because compaction reduces volume.
100mm or 150mm sub-base for a patio?
Domestic patios on reasonable ground commonly use 100mm; poor ground or vehicle use may require 150mm or more. This is a design decision — confirm with your contractor.
Do I need a membrane under the sub-base?
On soft or clay ground a separation geotextile between subgrade and sub-base stops the layers mixing and the stone pumping into the soil. On firm, well-drained ground it is often omitted. Follow your design or contractor's advice.