Groundwork in the right order
Almost every patio, drive, shed base or extension starts the same way: dig out, get rid of the spoil, lay and compact a sub-base, then add concrete, paving or gravel on top. The calculators above cover each step, and the project planners chain them together so you only enter your measurements once.
Volumes, tonnes and bags
Groundwork materials are sold in different ways. Concrete is ordered in cubic metres, sub-base and gravel by the tonne or 850kg bulk bag, and cement in 25kg bags. Each calculator converts your area and depth into all of these, using typical densities, and adds an allowance for compaction and waste.
- Concrete and foundations: slabs, strip footings and post holes.
- MOT Type 1 and gravel: sub-base, paths and decorative gravel.
- Patios and block paving: slabs, blocks, bedding and jointing.
- Excavation: how much spoil comes out and how to get rid of it.
Get the depth right
Under-building the sub-base is the most common reason patios sink and drives rut. Read the sub-base depth guide before you dig, and remember to allow for the paving and bedding layer when setting your finished levels below the damp-proof course.