They answer the quick questions that come before a proper estimate: how many bricks for a boundary wall, how much concrete for a slab, what a house of a given size is likely to cost in a given province, what the bond repayment and transfer duty will be. The material calculators use South African benchmark rates, so the cost they return is a guide to check a supplier quote against, not a replacement for one.

When you need more than a calculator

For a whole building, start with the cost per m² by city. For a tender, the tender pricing calculator shows the mark-up in your price, and the BoQ pricer prices the bill itself. The tender pricing guide walks through the build-up from direct cost to submitted price.

Get the quantity right first

Most wrong answers come from the measurement, not the rate. Measure from the drawings rather than from memory, keep units consistent (millimetres for thickness, metres for length), and deduct openings from wall areas. Each calculator states the waste allowance it adds, so do not add your own on top unless your site justifies it, such as a lot of cutting around an irregular plan.

From a result to a budget line

Write down the inputs next to every result you use, so anyone checking the budget can repeat the calculation. Round quantities up to the units you can buy: bags, sheets, cubes of sand, lengths of bar. Then add the items the calculator does not cover, such as delivery, hire of plant and the labour to prepare the area, before the figure goes into an estimate or a quote.

How current are the rates?

The material calculators name the benchmark source for their rates under each result, and the building cost calculator uses the same AECOM-based model as the cost pages. Prices move, and delivery to a remote site can add a lot, so treat any cost as a check on the quotes you receive. For monthly movement in material prices, read The Rate Sheet.