Concrete Calculator
Use our Concrete Calculator to quickly calculate how much concrete you need for slabs, foundations, posts, or other projects.
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Frequently Asked Questions
What is the standard ratio for mixing concrete?
A standard general-purpose concrete mix in the UK (C20) is usually 1 part cement, 2 parts sharp sand, and 4 parts 20mm gravel (1:2:4). Add water until the mix is workable but not sloppy.
How deep should a concrete base be?
For a garden shed base or patio, 100mm (4 inches) of concrete is usually sufficient. For a driveway taking vehicles, you should aim for a minimum of 150mm (6 inches) on a firm sub-base.
Do I need a sub-base under concrete?
Yes, for any load-bearing slab like a driveway or large shed, a compacted MOT Type 1 aggregate sub-base of at least 100mm is strongly recommended to prevent cracking and subsidence.
How long does concrete take to cure?
Concrete takes 24 to 48 hours to set enough to walk on, but it takes 28 days to reach its full structural strength. Keep it damp during the first week to prevent cracking.