- ~10m²20mm gravel at 50mm
- ~4m²MOT Type 1 at 100mm
- ~20m²sharp sand at 25mm
- ~5m²all-in ballast at 100mm
Coverage of one 850kg bulk bag
m² covered at each depth, no allowance for waste.
| Material | 25mm | 50mm | 75mm | 100mm | 150mm |
|---|---|---|---|---|---|
| 20mm gravel | 20.6 | 10.3 | 6.9 | 5.2 | 3.4 |
| 10mm pea shingle | 21.2 | 10.6 | 7.1 | 5.3 | 3.5 |
| Slate chippings | 24.3 | 12.1 | 8.1 | 6.1 | 4.0 |
| Sharp sand | 20.6 | 10.3 | 6.9 | 5.2 | 3.4 |
| All-in ballast | 19.4 | 9.7 | 6.5 | 4.9 | 3.2 |
| MOT Type 1 (compacted) | 16.2 | 8.1 | 5.4 | 4.0 | 2.7 |
The calculators add 5% for an uneven surface, so they buy one bag for up to about 9.8m² of gravel at 50mm.
Using a 1 tonne bag instead? Multiply by 1.18. An 800kg bag: multiply by 0.94.
The sum
Coverage (m²) = bag weight (t) ÷ (density (t/m³) × depth (m))
20mm gravel at 50mm: 0.85 ÷ (1.65 × 0.05) = 10.3m²
For your own area, use the gravel calculator (gravel, sand, ballast) or the MOT Type 1 calculator.
