Concrete Calculator
Or mix your own, roughly: of 25 kg cement plus of all-in ballast (1:5 mix).
How much concrete do I need?
Enter the length, width and depth of the slab or footing and the calculator gives the volume in cubic metres, then the number of ready-mix bags in both 20 kg and 25 kg sizes, and roughly what it takes to mix your own from cement and all-in ballast at a 1:5 ratio. A 20 kg bag of ready-mix yields only about 0.0093 cubic metres, so bags suit small jobs like setting a post or a small pad.
For anything over about half a cubic metre, mixing from cement and ballast, or ordering ready-mixed by the barrow load, works out far cheaper and less back-breaking than dozens of bags. A typical path or shed base is 75 to 100 mm deep, a driveway 100 mm or more. Always order a little extra, as you cannot pause a pour to fetch more.
Frequently asked questions
Is the concrete calculator free?
Yes. It is completely free, with no sign-up and nothing to install. It runs entirely in your browser.
How accurate is it?
It gives a reliable estimate for ordering based on standard UK figures, but real quantities vary with ground conditions, wastage and how materials settle. Always add a margin and confirm with your supplier before buying.