Overview
Because hardcore is compacted in layers, the depth you enter should be the finished compacted depth. (Sub-base specifications historically sat under MCHW Series 800, restructured September 2025 — check the current Specification for Highway Works where a specification applies.)
How the calculation works
Hardcore weight = area × compacted depth × planning density, with 6F2 and crushed concrete around 2.0 t/m³ and limestone Type 1 around 2.2 t/m³.
Compaction shrinks loose volume — typically by a factor that depends on grading and plate compaction effort — so a loose m³ delivers less than a compacted m³ of finished layer.
The optional compaction allowance converts a compacted-layer target into a loose-order quantity: order tonnes = compacted tonnes × (1 + compaction % ÷ 100).
Worked example
A shed base 4m × 3m needs 100mm of compacted hardcore from 6F2 at 2.0 t/m³.
Area = 12 m², volume = 12 × 0.10 = 1.20 m³, weight = 1.20 × 2.0 = 2.40 tonnes compacted.
Adding a 15% allowance for compaction losses and uneven ground suggests ordering about 2.76 tonnes — four 850kg bulk bags (2,760kg needs four bags; three would leave you 210kg short) or a 3-tonne loose load.
6F2 / 6F5 crushed aggregate at a glance
- Planning density2.00 t/m³
- Typical range1.80–2.20 t/m³
- CategoryRecycled
- CompactionOften relevant
- SourcePlanning value based on typical UK 6F2 bulk densities
- Reviewed2026-08-16
Planning values for typical UK supplies; your supplier product data takes precedence.
6F2 / 6F5 crushed aggregate coverage guide
| Depth | Area per tonne | Area per 850kg bag | Weight per m² |
|---|---|---|---|
| 25mm | 20.0 m² | 17.0 m² | 50 kg |
| 40mm | 12.5 m² | 10.6 m² | 80 kg |
| 50mm | 10.0 m² | 8.5 m² | 100 kg |
| 75mm | 6.7 m² | 5.7 m² | 150 kg |
| 100mm | 5.0 m² | 4.3 m² | 200 kg |
| 150mm | 3.3 m² | 2.8 m² | 300 kg |
Computed from a 2.00 t/m³ planning density on level ground.
Assumptions and accuracy
Planning densities assume typical UK hardcore supplies; recycled products vary most because composition differs between suppliers.
No single compaction percentage is universal — it depends on material grading, moisture and the equipment used.
For load-bearing, highway or structural 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 |
How to use this calculator
- Measure the area to be covered and enter the finished compacted depth.
- Choose the hardcore material your project specifies.
- Open Advanced options and enable the compaction allowance to convert compacted tonnage into an order quantity.
- Add delivery pricing to compare bulk bag and loose-load costs.
When hardcore is commonly used
Hardcore underlies patios, driveways, shed bases and floor slabs, fills holes and levels sites. 6F2 and crushed concrete are economical general hardcore; MOT Type 1 is the graded sub-base where a specification calls for it.
Frequently asked questions
How much hardcore do I need?
For a 100mm compacted layer, allow 0.1 m³ per square metre — about 200kg of 6F2 or 220kg of MOT Type 1 per m² before allowances. Multiply by your area, or use the calculator above.
How much extra hardcore should I order for compaction?
A compaction and ordering allowance of 10-20% is common, but the right figure depends on the material, moisture and how well the subgrade was prepared. The calculator keeps this as an explicit, adjustable percentage.
Is 6F2 the same as MOT Type 1?
No. 6F2 is a coarser recycled hardcore used for fill and capping; MOT Type 1 is a graded sub-base material referenced in UK highway specifications. Use Type 1 where a drawing or specification calls for it.
How many tonnes of hardcore in a bulk bag?
Most hardcore bulk bags hold 850kg, not a full tonne, so a 'tonne bag' is usually about 0.85 tonnes. Check the printed net weight before ordering.
Can I use road planings as hardcore?
On many private jobs, yes — planings compact well for hardstanding and tracks. Use can be restricted near watercourses and drainage due to tar/bitumen content, so confirm acceptability for your site and disposal rules with your supplier.
References and source notes
- Recycled hardcore composition and density guidance from UK supplier data sheets (planning values).
- Standards for Highways — current Specification for Highway Works (MCHW, restructured September 2025; granular sub-base formerly under Series 800) — standardsforhighways.co.uk