Guide

Concrete Mix Ratios Explained for DIY

Getting the concrete mix ratio right matters for strength and durability. Here are the common ratios for DIY jobs and how to work out how much you need.

The standard ratios

A general-purpose mix for paths and shallow slabs is often 1 part cement to 2 parts sand to 4 parts coarse aggregate (1:2:4). For foundations and footings, a slightly stronger 1:2:3 is common. For setting fence posts, a dedicated postmix is easiest — it's poured dry into the hole and set with water.

Bagged all-in ballast

For small jobs, bags of ready-mixed concrete or all-in ballast (sand and aggregate pre-combined) save measuring. You just add cement in the right proportion, or with ready-mix, only water. It's more expensive per cubic metre but far more convenient for a few post holes or a small repair.

Working out quantities

Concrete is calculated by volume — length times width times depth in metres. Our concrete calculator turns your dimensions into a volume and the number of 20kg bags, with a waste allowance for uneven ground.

When to order ready-mix

Bags make sense up to about half a cubic metre. Beyond that, the cost and effort of mixing by hand climbs steeply, and a ready-mix delivery or mix-on-site lorry becomes both cheaper and far quicker. For a big slab, it also gives a consistent mix throughout.