Why this site exists
Most quantity calculators online are American. They think in feet, yards and 80 lb bags, and they assume products that are not sold here. The Australian ones are mostly built by suppliers to sell a particular product, or by software companies that have never ordered a truck of concrete and had it come up short.
BuildMaths is the set of calculations a builder actually runs before placing an order, written down with the assumptions showing. Every calculator states what it assumes, walks through a worked example, and includes a note on what a builder adds on top of the raw number and why. If a figure on this site is wrong, the assumptions panel is where you will find out.
Who makes it
BuildMaths is written by Stuart Burgess, a registered domestic builder in Victoria with two decades on site, who runs a small building company on Victoria's Surf Coast. The waste allowances, coverage rates and rules of thumb on this site are the ones used on that company's jobs, checked against manufacturers' published figures where they exist.
The site is independent. It is not affiliated with any supplier or manufacturer, and no calculator is tuned to favour a product. It is funded by advertising, which is why you will see ads on some pages, and it may in future include links to retailers that pay a small commission on sales. Neither changes the numbers.
What it is not
These are quantity estimators. They are not structural design, they are not a quote, and they do not replace your engineer's drawings, the NCC, or the instructions on the bag. Read the disclaimer before you order anything on the strength of a number here, and always confirm the final order with the supplier.
Corrections
If you find an error, or a product size that has changed, please get in touch. Corrections are made and dated on the page.