Tonnes and bulk bags
Volume = area × depth. Tonnes = volume × density. Densities are typical merchant figures — change them to the supplier's figure if you have it.
Estimates using typical densities. Moisture, grading and compaction change the weight per m³ — confirm with the supplier before ordering.
Aggregate densities and coverage
Typical loose densities quoted by UK merchants; the Type 1 figure is for the compacted layer.
| Material | Used here | Typical range |
|---|---|---|
| MOT Type 1 sub-base (compacted) | 2.1 | 2.0–2.2 |
| Sharp sand | 1.6 | about 1.6 |
| Building (soft) sand | 1.54 | about 1.5–1.6 |
| 20 mm gravel / shingle | 1.6 | about 1.6 |
| All-in ballast | 2 | about 2.0 |
| Topsoil | 1.3 | 1.1–1.3 |
| Depth | Type 1 | m² per 850 kg bag | Sand / gravel | Topsoil |
|---|---|---|---|---|
| 50 mm | 0.11 t | 8.1 m² | 0.08 t | 0.07 t |
| 75 mm | 0.16 t | 5.4 m² | 0.12 t | 0.10 t |
| 100 mm | 0.21 t | 4.0 m² | 0.16 t | 0.13 t |
| 150 mm | 0.32 t | 2.7 m² | 0.24 t | 0.20 t |
| 200 mm | 0.42 t | 2.0 m² | 0.32 t | 0.26 t |
Bulk bags are sold by weight (usually 800–900 kg), so their volume depends on the material — a bag of topsoil goes further than a bag of Type 1.
How to work out aggregate
Volume and tonnes
Area (m²) × depth (m) gives cubic metres; × density gives tonnes. A 5 × 4 m base of Type 1 at 100 mm compacted is 20 × 0.1 = 2 m³ × 2.1 = 4.2 t, about 4.6 t with a 10% allowance — six 850 kg bulk bags.
Compaction
Type 1 loses volume when it is rolled or wackered. The 2.1 t/m³ figure is for the finished, compacted depth, so enter the depth you want after compaction. On deeper bases lay and compact it in layers.
Allowance
Add about 10% for uneven formation, losses at the edges and material left in the bag. Soft spots dug out and refilled will need more.
Questions groundworkers ask
How much Type 1 do I need?
Multiply area by compacted depth to get m³, then by about 2.1 t/m³. For 20 m² at 100 mm that is 2 m³, about 4.2 t, or 4.6 t with 10% extra — six 850 kg bulk bags.
How many tonnes in a cubic metre of sand?
Sharp sand is typically about 1.6 tonnes per m³ and building sand a little less, depending on how wet it is.
How much does a bulk bag of Type 1 cover?
An 850 kg bag of Type 1 covers roughly 4 m² at 100 mm compacted depth, about 2.7 m² at 150 mm and 8 m² at 50 mm.
How much does a cubic metre of topsoil weigh?
Typically about 1.1 to 1.3 tonnes, more when wet. Many suppliers sell topsoil by the bulk bag or by volume rather than weight.
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See Graftum for groundworksTypical densities; confirm weights with the supplier before ordering.