Concrete calculator (m³ and bags)
Cubic metres to order, or how many 20 kg bags, for a slab, strip footing or piers.
A free tool from Footing Tools. No account needed. It works out one pour — Footing, the software, runs the whole job.
In ChatGPT
Describe the job in your own words. Find Footing Tools in ChatGPT.
Coming soon to ChatGPTIn Claude
Same tools, same documents. Find Footing Tools in Claude.
Coming soon to ClaudeWork out the concrete
Starter prompts
Paste one into ChatGPT or Claude once Footing Tools is added.
“How much concrete for a 6x4 slab, 100mm thick?”
“Concrete for 8 round piers, 450mm wide and 900mm deep”
“How many 20kg bags for a 1.2x1.2m pad, 150mm thick?”
What it won't do
- Design footings or slabs. Use your engineer's specs for sizes and reinforcement.
- Price the concrete. Check with your supplier.
Templates and calculations only — not legal, financial, safety or professional advice. Check everything against your contract and the law, or get advice, before you rely on it. Footing isn't responsible for how it's used.
Straight answers
How do I work out cubic metres of concrete?
Length × width × depth in metres, plus a waste allowance. For a 6 × 4 m slab, 100 mm thick, that's 6 × 4 × 0.1 before waste. The calculator does it and shows each step.
Bags or a truck?
Bags suit small pours like pads and post holes. For a slab, order by the cubic metre. The calculator gives you both so you can decide.
What about piers?
Pick round or square piers, add the size, depth and how many. It adds them up.
Running more than a few jobs?
This works out one pour. Footing measures off your plans and turns the quantities into a quote, or a request for quotes your suppliers can price from their phone.