Calculation methodology

Formulas

All calculations convert inputs to SI units (metres, square metres, cubic metres) before any arithmetic, then convert results back to your regional units. Conversion factors are exact legal definitions (for example 1 inch = 0.0254 m).

Discrete products such as sheets, boards and bags round up to whole purchasable units. Bulk materials stay at the calculated quantity unless the calculator asks for a supplier ordering increment; no universal quarter-unit rule is assumed.

Every formula has automated tests including hand-calculated worked examples. The formula version is displayed on each calculator page and incremented on any change.

Prices and taxes

This site does not publish live material prices. Price fields are blank and editable — enter a quote from your local supplier. Where an example figure appears it is clearly labelled as an illustration, not a market average.

A cost result distinguishes tax-inclusive, tax-exclusive and not-yet-confirmed quotes. Enter the basis shown on your supplier quote; when the basis is not confirmed, the calculator keeps tax out of the final total rather than silently guessing.

What estimates are not

Estimates are not quotations, structural designs, code-compliance checks or professional advice. Wastage, site conditions, and product variations mean real projects can differ. Always confirm quantities with your supplier before ordering.