Depth guide
Gravel depth by project
Pick a sensible finished depth before calculating gravel bags, tonnes, or bulk loads.
Compare planning depths for decorative gravel, garden paths, driveways, and base layers before estimating gravel quantity.
Start with the job, not the bag size
The same area can need very different quantities if one project is a decorative border and another is a driveway. Choose the finished gravel layer first, then calculate volume. If the project also needs a compacted sub-base, treat that as a separate material estimate rather than adding it to the decorative gravel depth.
- Decorative borders usually need enough depth to hide membrane and give even coverage.
- Paths need enough depth to stay consistent after foot traffic and small settlement.
- Driveways and bases need separate checks for sub-base, drainage, and compaction.
Use depth as a planning assumption
A calculator can show the effect of changing depth very clearly. Increasing depth from 4 cm to 6 cm increases the volume by 50%, so a small-looking depth change can become several extra bags on a larger project. Record the depth you used so a supplier can sense-check the order.
- Run the calculator at the shallow and deep end of your likely range.
- Compare the difference in tonnes as well as bag count.
- Keep load-bearing advice separate from decorative coverage estimates.
Planning depth comparison
| Project type | Depth assumption to test | Extra check |
|---|---|---|
| Decorative border | 3-5 cm | Membrane, edging, and stone size. |
| Garden path | 4-7.5 cm | Traffic level, edging, and base preparation. |
| Driveway top layer | Project-specific | Sub-base, drainage, compaction, and vehicle load. |
| Shed or bin-store base | Often separate base layers | Confirm compacted material rather than loose decorative gravel. |
This is an estimate. Site conditions, compaction, and aggregate type can change the final quantity.