Quantities
How much sub-base do I need?
4 min read
How do I calculate how much sub-base I need?
Multiply the area in square metres by the compacted depth in metres to get cubic metres, then allow roughly 10-15% extra because granular material compacts and settles. Typical compacted depths are around 100mm for footpaths and patios and 150mm or more for driveways, subject to your ground conditions.
Start with area and depth
Sub-base quantities come from a simple volume sum. Measure the area you are covering in metres, multiply length by width to get square metres, then multiply by the compacted depth expressed in metres.
For example, a patio 5m x 4m with a 100mm compacted sub-base is 5 x 4 x 0.1 = 2 cubic metres of compacted material.
Allow for compaction
Granular sub-base is delivered loose and reduces in volume once it is whacked down. As a working rule, add 10-15% to the compacted figure so you are not short on the day. Uneven ground, soft spots and deeper edge details all increase the amount you need.
Typical depths
- Foot traffic only (paths, patios): commonly around 100mm compacted.
- Cars (driveways): commonly 150mm or more compacted.
- Soft or clay ground: often deeper, sometimes with a geotextile membrane below.
These are general guides, not a specification. Ground conditions vary from one street to the next, so if your subsoil is soft, wet or made ground, get advice before you set your depth.
Converting volume to what you order
Aggregates are sold by weight or by bag depending on the product, so a cubic metre figure needs converting before you can order. The conversion depends on the material and its moisture content. Tell us your cubic metre figure and we will confirm how much to order in the unit the product is sold in.
Not sure what to order? Send your measurements through our quote form and we will work the quantities out with you, or call the yard on 01483359553.