How We Research, Calculate and Correct

Where the formulas come from

No calculator on this site invents a coefficient. Each one is written as a pure, deterministic function whose constants are traceable to a published trade standard, a manufacturer's own technical datasheet, or a documented code requirement. Where a standard gives a range rather than a single number — waste allowance for a herringbone tile lay, for instance — we take the range and state it openly on the calculator page rather than silently picking the middle.

Why our numbers are higher than bare geometry

Multiplying length by width tells you the area of a room. It does not tell you how much material to buy, and estimators who stop there run short on site. Three things sit between the two numbers:

• Cut geometry. A perimeter cut wastes the offcut unless it happens to fit the opposite wall. Diagonal and herringbone layouts produce two angled offcuts per tile instead of one square one, which is why our waste band rises from 10% to 20% across those patterns rather than staying flat.
• Unit indivisibility. Flooring is sold by the carton, cement by the bag, timber by the length. We round up to the purchasable unit, never to the nearest, because a floor that is three planks short is a second trip and often a second dye lot.
• Substrate reality. Screw spacing, deflection limits and mortar coverage are set by code and by the substrate, not by the finish area. These are counted separately rather than folded into a single per-square-foot figure.

Each calculator shows its own working under How this is calculated so you can check the assumption rather than trust the output.

Review and update cadence

• Cost guides are re-costed at least twice a year, and sooner when a material moves sharply. The publication and last-updated dates on every guide are real, not refreshed automatically to look current.
• Formulas are re-checked when the underlying standard is revised. When a referenced standard is superseded, the calculator is updated and the change noted on the page.
• Reported errors are triaged within two business days and corrected in place, with the guide's dateModified advanced so readers can see it changed.

Regional content

Building practice is not universal. A UK bathroom is tiled over suspended timber with a decoupling mat; an Indian one is tiled onto a 30mm cement mortar bed; an American one is usually over a slab or ply subfloor with thin-set. Where we publish regional guidance, it is written against that market's own product sizes, purchase units and standards — 20kg adhesive bags and BS 5385 for the UK, 50kg cement bags and IS 456 for India, AS/NZS references for Australia.

Regional variants exist to serve readers who need those conventions, not to multiply pages. They are deliberately excluded from search indexing so that the primary calculator remains the single canonical answer for a given tool, and you can switch region on any calculator using the region selector without leaving the page.

Independence and funding

The site is free to use and carries no registration wall, no lead-generation form and no sale of contact details to contractor networks. Calculations run entirely in your browser; dimensions and budgets you enter are never transmitted to a server. Running costs are covered by display advertising, which is kept out of the calculator input flow and clearly labelled.

No manufacturer, merchant or contractor pays for placement, and no recommendation on this site is sold. Where a specific product is named it is because it is the standard reference in that trade, not because of a commercial arrangement.