Gravel calculator
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Work out how many tonnes and bulk bags of gravel to order. Enter your measurements below; every figure we start from is shown and you can change it.
Worked example
| You enter | Value |
|---|---|
| Area | rectangle 5 m × 4 m |
| Depth | 50 mm |
| Material | Gravel or pea shingle |
| Density | 1.6 t/m³ |
| Waste allowance | 5% |
| Bulk bag size | 0.85 t |
| Small bag size | 25 kg |
Order: 2 bulk bags
| Result | Value |
|---|---|
| Bulk bags | 2 |
| Small bags | 68 |
| Weight | 1.68 t |
| Volume (with waste) | 1.05 m³ |
| Area | 20 m² |
Show the working
- Area: Area 1 20 m² = 20 m²
- Volume: 20 m² × 0.05 m = 1 m³
- With 5% waste: 1 × 1.05 = 1.05 m³
- Weight: 1.05 m³ × 1.6 t/m³ = 1.68 t
- Bulk bags: 1.68 t ÷ 0.85 t = 1.98, rounded up to 2
- Small bags: 1,680 kg ÷ 25 kg = 67.2, rounded up to 68
How it works
- Volume (m³) = area (m²) × depth (m) × (1 + waste)
- Weight (t) = volume (m³) × density (t/m³)
- Bulk bags = weight (t) ÷ bulk bag size (t), rounded up
- Small bags = weight (t) × 1,000 ÷ small bag size (kg), rounded up
Densities differ between sources, so the range is shown. Your supplier's figure takes precedence.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Density: Gravel or pea shingle | 1.6 t/m3 Sources range 1.6–1.75 t/m3 | Typical value Not yet checked against the source | agg.directory calculator; aggregatecalculator.co.uk density table (checked 19 October 2026) Gravel and pea shingle. Sources differ, so the range is shown. |
| Density: Decorative stone | 1.5 t/m3 Sources range 1.3–1.7 t/m3 | Typical value Not yet checked against the source | aggregatecalculator.co.uk aggregate density table (checked 19 October 2026) Decorative stone varies with stone type. |
| Waste allowance | 5 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job Spreading and settling; compaction varies. |
| Bulk bag size | 0.85 t | Common UK size Not yet checked against the source | builder.tools bulk bag figure (checked 19 October 2026) Varies by merchant; check yours. |
| Small bag size | 25 kg | Common UK size Not yet checked against the source | From your product Common small bag. |
FAQs
Guides
Bulk bags vs loose loads
Bulk bag sizes vary by merchant. How access and quantity decide between bulk bags and loose loads, and how to compare per tonne.
How much gravel do I need?
Turn area and depth into tonnes and bulk bags of gravel, why suppliers sell by weight, and what depth to use for paths and drives.