Concrete Footing Calculator
Work out how much concrete you need for a footing or slab. Enter the area, the calculator returns the number of 20kg bags (with waste) and an indicative cost, based on a typical depth.
How we estimate this
A 20kg bag of concrete mix yields only about 0.009 cubic metres, so it covers roughly 0.09 square metres at 100mm. Bags add up fast, even a small 5m² slab at 100mm needs around 55 to 60 bags.
Pricing reviewed: November 2026.
Pricing reviewed November 2026. Indicative Australian costs, not a quote.
Understanding concrete footings in Australia
A 20kg bag of concrete mix yields only about 0.009 cubic metres, so it covers roughly 0.09 square metres at 100mm. Bags add up fast, even a small 5m² slab at 100mm needs around 55 to 60 bags.
Past about half a cubic metre (roughly 5m² at 100mm, or a few metres of footing), a pre-mixed concrete delivery is far cheaper and faster than mixing bags by hand, and gives a more consistent pour. Price both for anything above a tiny job.
Frequently asked questions
How many bags of concrete do I need for a footing?
A 20kg bag covers only about 0.09m² at 100mm depth, so even a small 5m² slab needs around 55 to 60 bags. Deeper footings use proportionally more.
When should I order pre-mixed concrete instead of bags?
Past about half a cubic metre (roughly 5m² at 100mm), pre-mixed delivery is cheaper, faster and more consistent than mixing bags. Below that, bags are fine.
Are you a concrete supplier / concreter?
Everyone on this page is working out what concrete footing costs because they are ready to hire. Put your business right beneath the calculator, in your state, so you are who they find. From $50/mo.