Driveway gravel depth planning guide

Depth depends on use

Decorative gravel, footpaths, and driveways are not the same job. The calculator estimates quantity after you choose a depth.

• Decorative borders often use shallower depths.
• Paths need enough depth to cover the base evenly.
• Driveways may need sub-base and construction guidance before top gravel is added.

Measure the finished surface

Use the length and width of the area that will actually be covered, after edging and borders are set.

• Split irregular areas into rectangles where possible.
• Use average depth when the ground is uneven.
• Allow for settling, edging losses, and compaction.

Gravel depth by project

Pick a sensible finished depth before calculating gravel bags, tonnes, or bulk loads.

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

The planning depth comparison reference keeps the relevant comparisons together so each assumption can be checked before changing the calculator inputs.

• Project type: Decorative border; Depth assumption to test: 3-5 cm; Extra check: Membrane, edging, and stone size.
• Project type: Garden path; Depth assumption to test: 4-7.5 cm; Extra check: Traffic level, edging, and base preparation.
• Project type: Driveway top layer; Depth assumption to test: Project-specific; Extra check: Sub-base, drainage, compaction, and vehicle load.
• Project type: Shed or bin-store base; Depth assumption to test: Often separate base layers; Extra check: Confirm compacted material rather than loose decorative gravel.

Sub-base vs decorative gravel

Keep decorative gravel estimates separate from load-bearing sub-base estimates.

They are different layers

Decorative gravel is usually the visible top layer. A sub-base is a compacted layer below it, often used to spread load, improve stability, and support the finished surface. Mixing these two layers into one calculator run can make the result misleading because the depth, density, and purpose are different.

• Use decorative aggregate density for visible gravel, chippings, or pea gravel.
• Use a denser preset such as MOT Type 1 only when estimating that specific base material.
• Calculate each layer separately if the build-up has more than one material.

Why density matters

A cubic metre of one aggregate type may not weigh the same as a cubic metre of another. The calculator includes density so that a top layer of slate chippings, a pea gravel path, and a compacted sub-base estimate can be handled differently. Supplier figures should take priority where available.

• Check whether the supplier lists tonnes per cubic metre, kg per bag, or coverage per bag.
• Use the custom density field when the supplier gives a better figure.
• Do not use a decorative gravel estimate as construction advice for structural work.

Layer comparison

The layer comparison reference keeps the relevant comparisons together so each assumption can be checked before changing the calculator inputs.

• Layer: Visible gravel; What to calculate: Finished top layer volume and bag count; Common mistake: Forgetting edging losses or settlement.
• Layer: Sub-base; What to calculate: Separate compacted base volume and weight; Common mistake: Using decorative gravel density for base material.
• Layer: Membrane and edging; What to calculate: Usually not part of gravel volume; Common mistake: Measuring before edging reduces the finished area.

Depth planning examples