Calculation Methodology

Our calculators use straightforward geometry and material relationships such as area ÷ coverage, volume × bulk density, or area × units per square metre. Where a calculator needs a typical material value, we label it as an assumption and make it editable where practical. Manufacturer data should take priority over our defaults.

Calculation hierarchy

We first calculate a physical area or volume, then apply a coverage, density, yield or unit rate. Purchase quantities are rounded up only at the final step. This avoids compounding rounding errors.

Default assumptions

Defaults are deliberately editable. They are intended to make a calculator usable immediately, not to represent every product. Manufacturer values should take priority whenever available.

Waste allowances

Waste is shown separately so it can be changed rather than hidden inside a formula. Different projects require different allowances, and adding a blanket percentage twice is a common source of over-ordering.

Units and rounding

Calculations use consistent base units internally. Continuous quantities such as litres or cubic metres are displayed to a practical precision; indivisible purchase units such as bags, tiles, rolls and packs are rounded up.