Aggregate Calculator Guide

Types of Aggregate

MOT Type 1

Crushed limestone or granite, graded 0-40mm. The standard sub-base material for UK construction.

• Use: Under driveways, patios, block paving, concrete slabs
• Why: Compacts to a solid, load-bearing layer
• Density: 2.0 tonnes/m³ (loose)
• Cost: £25-35 per tonne loose, £35-45 per bulk bag

Hardcore (Type 2 / Crusher Run)

Recycled crushed concrete and brick. Cheaper alternative to MOT Type 1.

• Use: Light-duty bases (sheds, greenhouses, garden paths)
• Why: Cheaper, environmentally friendly (recycled)
• Density: 1.9 tonnes/m³ (varies more than MOT)
• Cost: £18-28 per tonne
• Downside: Less uniform, not suitable for driveways

Gravel / Decorative Aggregate

Rounded stones for gravel driveways, paths, and borders.

• Use: Decorative surface (not a sub-base)
• Types: Pea gravel (10mm), 20mm gravel, slate chippings
• Density: 1.7 tonnes/m³
• Cost: £40-80 per tonne (decorative is expensive)
• Depth: 40-50mm for paths, 75mm for driveways

Sharp Sand

Coarse sand for bedding layer under block paving and slabs.

• Use: 30-50mm bedding layer
• Density: 1.6 tonnes/m³
• Cost: £30-45 per tonne
• Not building sand: Building sand is too fine, doesn't compact

Recommended Depths

Calculating Tonnage

Formula

Tonnes = Area (m²) × Depth (m) × Density (tonnes/m³) × Compaction factor

Compaction Factor

Loose aggregate compacts down when vibrated/rolled. Order 20-25% more than the volume calculation suggests.

Compaction factor = 1.25 (i.e. order 25% more)

Worked Example

Driveway: 10m × 3m, 150mm deep MOT Type 1

• Area: 10 × 3 = 30 m²
• Depth: 150mm = 0.15m
• Volume: 30 × 0.15 = 4.5 m³
• Tonnes (loose): 4.5 × 2.0 = 9 tonnes
• With compaction: 9 × 1.25 = 11.25 tonnes
• Order: 11.5 tonnes

Bulk Bags vs Loose Tonnes

Bulk Bags (Jumbo Bags)

• Typically 800-1000kg per bag (call it 0.85 tonnes average)
• Delivered on pallet, crane-lifted into place
• £35-50 per bag (£40-60 per tonne equivalent)
• Best for: Under 3 tonnes, limited access, phased projects

Loose Tonnes

• Tipped from lorry into your drive
• £20-35 per tonne (much cheaper for large orders)
• Minimum order usually 6-8 tonnes
• Best for: Over 3 tonnes, you have space to store it

Cost Comparison (11.5 tonnes for driveway above)

• Bulk bags: 14 bags × £42 = £588
• Loose tonnes: 11.5 tonnes × £28 = £322
• Saving: £266 by ordering loose

Membrane (Geotextile Fabric)

Lay weed-suppression membrane under MOT Type 1 to prevent mixing with soil.

• Stops aggregate sinking into soft ground
• Prevents weeds growing through
• £15-30 per 50m roll (covers ~50 m²)

Do You Need Edging?

For gravel driveways and paths, yes. Gravel doesn't compact, so it spreads without edging.

• Timber edging: £5-10 per metre
• Metal/plastic edging: £8-15 per metre
• Concrete kerbs: £12-25 per metre

For MOT Type 1 under slabs/paving, edging not essential (the paving holds it in place).

Delivery Access

Aggregate lorries are large:

• Need 3m+ width to get down drive
• Can't reverse more than ~20m
• Tipping loose aggregate needs space (it forms a cone ~2m high)

No access? Bulk bags can be crane-lifted over fences/walls (extra £30-50 charge).