Material choice
Sub-base vs decorative gravel
Keep decorative gravel estimates separate from load-bearing sub-base estimates.
Understand when to calculate decorative gravel separately from MOT Type 1 or another compacted sub-base material.
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
| Layer | What to calculate | Common mistake |
|---|---|---|
| Visible gravel | Finished top layer volume and bag count | Forgetting edging losses or settlement. |
| Sub-base | Separate compacted base volume and weight | Using decorative gravel density for base material. |
| Membrane and edging | Usually not part of gravel volume | Measuring before edging reduces the finished area. |
This is an estimate. Site conditions, compaction, and aggregate type can change the final quantity.