Overview
This guide gives typical depths for common UK projects so you can sanity-check a calculation or brief a supplier.
How the calculation works
Multiply the three: a 40 m² driveway sub-base at 125mm of Type 1 (2.2 t/m³) is 40 × 0.125 × 2.2 = 11 tonnes before allowance.
Depths by project: decorative dressings 40-50mm; footpaths 50-100mm; patios and shed bases 75-100mm; vehicle sub-bases 100-150mm (compacted).
Densities cluster in three bands: decorative gravels ~1.5, sands and gravels ~1.6-1.7, sub-base and hardcore ~2.0-2.2 t/m³.
Worked example
Garden path 15 m² at 75mm of gravel over firm ground: 15 × 0.075 × 1.6 = 1.8 tonnes; order 2 tonnes.
Patio 25 m² with 100mm Type 1 sub-base: 25 × 0.1 × 2.2 = 5.5 tonnes plus 15% compaction allowance = 6.3 tonnes.
Shed base 3m × 2.5m at 100mm hardcore: 7.5 × 0.1 × 2.0 = 1.5 tonnes compacted, order 1.75 tonnes.
Assumptions and accuracy
Depths above are common practice for reasonable ground, not engineering specifications.
Add 5-10% ordering allowance for dressings and 10-20% for compacted sub-bases on loose orders.
Confirm the specified layer depths and quantities with your contractor or supplier for firm orders.
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 area in square metres (length × width, or segment an L-shape into rectangles).
- Pick the depth for your project type from the guidance above.
- Multiply area × depth (in metres) × material density for tonnes.
- Add the allowance and check the result with the full calculator.
When aggregate is commonly used
Use this guide at the planning stage — sketching budgets and briefs — then move to the material-specific calculators for the numbers you actually order from.
Frequently asked questions
How much aggregate do I need for a driveway?
For the sub-base allow 220-330kg of Type 1 per m² (100-150mm compacted) plus 64-80kg per m² of gravel surfacing. A 50 m² drive totals roughly 13-17 tonnes of sub-base and 3.5-4 tonnes of gravel.
How much aggregate for a patio?
Typically 100mm of sub-base — about 220kg of Type 1 per m² — plus a 30-50mm sharp sand bedding course (48-80kg per m²).
How much extra should I order?
5-10% for decorative finishes and bedding sands; 10-20% for compacted hardcore and sub-bases ordered loose. The calculator applies whichever figure you choose and shows it separately.
How many bulk bags for a small patio?
A 20 m² patio at 100mm of compacted Type 1 needs about 5.5 tonnes — order around 6.3 tonnes with allowance, which is eight 850kg bulk bags or one small loose load.
References and source notes
- Typical layer depths summarised from UK trade practice; project-specific requirements vary.
- Standards for Highways — current Specification for Highway Works (MCHW, restructured September 2025; granular sub-base formerly under Series 800) — standardsforhighways.co.uk