BuildCalcs Volume before weight
For a rectangular area, volume = length × width × depth. Convert millimetres to metres before multiplying. A 6 m × 3 m area at 100 mm has a compacted geometric volume of 1.80 m³.
Volume reference table
| Area | 50 mm | 75 mm | 100 mm | 150 mm |
|---|---|---|---|---|
| 5 m² | 0.25 m³ | 0.38 m³ | 0.50 m³ | 0.75 m³ |
| 10 m² | 0.50 m³ | 0.75 m³ | 1.00 m³ | 1.50 m³ |
| 20 m² | 1.00 m³ | 1.50 m³ | 2.00 m³ | 3.00 m³ |
| 30 m² | 1.50 m³ | 2.25 m³ | 3.00 m³ | 4.50 m³ |
| 40 m² | 2.00 m³ | 3.00 m³ | 4.00 m³ | 6.00 m³ |
| 50 m² | 2.50 m³ | 3.75 m³ | 5.00 m³ | 7.50 m³ |
Why tonnes are less universal than cubic metres
Weight depends on bulk density, which varies with material, grading, moisture and compaction state. For that reason BuildCalcs treats any volume-to-weight conversion as an estimate based on the density value used. If your supplier provides a product-specific conversion or coverage figure, use that for ordering.
Worked driveway example
A 5.5 m × 4.0 m area is 22 m². At 100 mm, 22 × 0.10 = 2.20 m³ compacted geometric volume. If you then apply a bulking/ordering assumption, keep that assumption separate and labelled.
Compacted depth versus loose material
The target finished depth and the loose quantity delivered are not interchangeable. Material consolidates during compaction. This is why a calculator cannot guarantee the number of bulk bags or tonnes without assumptions about the actual product and installation.
Measure irregular areas sensibly
Split L-shaped drives or paths into rectangles, calculate each area, then add them. For tapered areas, a simple approximation using average width can be useful, but record that it is an approximation.
Before you order
- Use the intended compacted depth.
- Check the supplier's product-specific density or coverage.
- Allow for excavation variation where appropriate.
- Do not add the same allowance twice.
Enter your actual measurements rather than relying on a generic example.
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