Sub-Base Calculator | Estimate MOT Type 1, Hardcore & Aggregate Depths
Estimate required MOT Type 1 or hardcore volume, weight and bulk bags for patios, driveways or foundations.
Sub-Base Calculator Guide (Type 1, Scalpings, Gravel)
Plan compacted thickness, order the right loose volume, and estimate bulk bags, tonnes, and delivery. This guide pairs with the SmartBuildCalc Sub-Base Calculator.
Recommended Tools & Materials
- MOT Type 1 Bulk Bags — Travis Perkins
- Hire Wacker Plate Compactor — Travis Perkins
- Heavy Duty Weed Control Landscape Fabric - 2m x 25m- Wickes
- Builders Shovel & Rake Set — Amazon
- WheelBarrow — Travis Perkins
Disclosure: Some links may be affiliate links that help support SmartBuildCalc at no extra cost to you.
When & Why to Use a Sub-Base Calculator
- Patios, block paving, resin drives, paths, sheds, and garden rooms.
- Converts finished compacted depth into loose order volume (with waste).
- Outputs tonnes and bulk bags using realistic densities.
Recommended Depths by Application
| Application | Compacted Depth | Material | Notes |
|---|---|---|---|
| Paths & patios (pedestrian) | 75–100 mm | MOT Type 1 / scalpings | Compact in ≤75 mm lifts. |
| Block paving driveway | 100–150 mm | MOT Type 1 | Go 150 mm+ for heavier vehicles or soft sub-grade. |
| Resin bound driveway | 150 mm | MOT Type 1 + binder course | Follow resin system spec. |
| Shed / garden room | 75–150 mm | Type 1 / scalpings / gravel | Use geotextile over weak ground. |
Density & Compaction Factors
| Material | Density (kg/m³) | Compaction Factor | Notes |
|---|---|---|---|
| MOT Type 1 | ~2200 | 1.20–1.35 | High fines → tight compaction. |
| Scalpings | ~1900 | 1.20–1.35 | Cheaper, grading varies. |
| 20 mm gravel | ~1700 | 1.10–1.25 | Lower fines, lighter per m³. |
UK Price Guide (2025)
| Item / Service | Average Price (ex. VAT) | Notes |
|---|---|---|
| MOT Type 1 (loose per tonne) | £30 – £55 | Lower near quarries; higher in cities. |
| Scalpings (loose per tonne) | £25 – £45 | Good for light-duty paths. |
| Gravel 20 mm (loose per tonne) | £35 – £65 | Decorative grades cost more. |
| Bulk bag Type 1 (~850 kg) | £45 – £85 / bag | Local delivery often included. |
| Delivery (tipper / hiab) | £10 – £45 / drop | Hiab offload or timed slots extra. |
| Wacker plate hire | £25 – £45 / day | Weekend bundles available. |
| Grab hire (muck-away) | £180 – £420 / load | 8-wheel ~16–20 t; wet spoil costs more. |
| Geotextile membrane | £0.70 – £2.00 / m² | Woven = separation, non-woven = drainage. |
Worked Example
Job: 6 × 4 m patio at 100 mm compacted, MOT Type 1 (density 2200 kg/m³, compaction 1.25, waste 5%).
Approx loose material cost: £277 – £495 + delivery, depending on supplier and region.
Related Calculators
Frequently Asked Questions
How deep should a Type 1 sub-base be in the UK?
75–100 mm for paths/patios; 100–150 mm for driveways. Increase for soft ground or heavier vehicles.
How many bulk bags of Type 1 do I need per m²?
~0.6 m³ bag covers ~4.8 m² at 100 mm depth. Add 5–10% for waste and settlement.
How much does Type 1 cost?
£30–£55 per tonne loose, £45–£85 per bulk bag delivered, plus any delivery/hiab fees.
What compaction factor should I use?
Type 1: 1.20–1.35, Scalpings: 1.20–1.35, Gravel: 1.10–1.25. Check your supplier’s guidance.
Do I need geotextile?
It helps separate the sub-grade from the sub-base and reduces pumping on weak soils. Woven for separation, non-woven for drainage.
Note: Prices vary by region and season. Always confirm with local suppliers before ordering.
