About this site
A concrete calculator that gives you a number in seconds, on a phone, at a job site.
What this site is for
Most people arriving here have one question: how much concrete do I need? They are usually standing next to the job with a tape measure, on mobile data, and they want an answer before the page has finished loading.
So the calculator is the first thing on every page. There is no sign-up, no email capture, nothing to dismiss, and nothing between you and the result. Everything below the calculator is there for people who want to understand the number rather than just take it.
Who it is for
- Homeowners pouring a shed base, path, or a few fence posts.
- Tradespeople who want a quick second check before ringing the supplier.
- Anyone comparing a quote against what the volume should actually be.
Where the numbers come from
The maths is deliberately unremarkable, because concrete volume is not a complicated problem:
- Rectangular pours: length × width × depth, with all measurements converted to metres first.
- Post holes: π × radius² × depth, multiplied by the number of holes.
- Waste allowance: volume × (1 + allowance ÷ 100).
- Order quantity: the allowed volume rounded up to the next 0.2 m³, which is how most Australian suppliers sell.
- Bags: volume ÷ the yield of one bag, rounded up. The yield comes from the product, not from a guess based on weight.
Everything runs in your browser. No measurements are sent to a server.
What this site does not do
It estimates quantity. That is all. It does not tell you how thick your slab should be, what reinforcement it needs, what strength class to order, or whether your ground is suitable. Those depend on loads, soil classification, exposure and the applicable Australian Standards, and they need a person who can look at your site and take responsibility for the answer.
Where this site gives thickness examples, they are general illustrations to help you use the calculator, not a specification.
Accuracy, and how it is checked
Every formula these calculators use is written out in full on how we calculate — the volume arithmetic, the unit conversions, the waste allowance, supplier order increments, bag yields, and the rounding.
The arithmetic is not checked by eye. An automated test suite runs against the same code your browser loads, covering the worked examples, equivalent measurements in different units, invalid input, bag counts, order increments, and a floating-point case where the obvious way of rounding reports the wrong answer. A second suite checks the published site rather than the source: it loads each live page, runs the real calculator code, and confirms the numbers that appear on screen are the numbers expected.
That is the honest extent of it — careful arithmetic, checked continuously. The calculators have not been reviewed by a structural or civil engineer, and we do not claim otherwise. They are provided as-is and without warranty. Always confirm final quantities with your supplier before ordering; they do this every day and it costs nothing to ask.
If you spot something wrong, tell us. Include the numbers you entered, the units you chose, the result you got and the result you expected. Corrections are welcome and get fixed quickly.
How the site is paid for
This site is free to use and is funded by advertising through Google AdSense. Ads are kept away from the calculator inputs and results, are never dressed up to look like buttons or results, and are not placed where they can cause you to mis-read a number. If an ad ever gets in the way of the calculation, that is a bug — please report it.