About this site
Anyone can put a formula behind a text box. What follows is how this site tries to earn a number being trusted — and, just as importantly, where it says it cannot be.
One engine, not many pages
Every calculator is a declaration: its inputs, a pure function that turns those inputs into a result, the standards it cites, its test cases and its FAQ. A single renderer turns any of those declarations into a working page.
The practical consequence is that an improvement lands everywhere at once. When the unit handling was corrected, every calculator was corrected. There is no page carrying an old version of a shared behaviour, because there is only one copy of it.
Every formula names its source
A result you cannot check is a result you should not use. Each calculator lists the standards behind it with the clause or section number, so the arithmetic can be traced back to a document that has authority — ACI, IRC, NEC, IPC, ASHRAE, Eurocode, AS/NZS and BS, depending on the subject and the market.
Where no standard exists, or where the honest answer depends on data the site does not have, the page says so instead of estimating. That is why some calculators state a limitation rather than producing a confident figure: a plausible number in that position is worse than an absent one.
What lastVerified means
It is the date the cited sources were last checked against the calculation — not the date the page was published, and not a promise that the standard has not changed since.
Codes move on cycles. A clause that was current when checked can be superseded, and nothing here notices automatically. Treat the date as what it is: the last time a person confirmed the citation, and the point from which you should verify anything load-bearing yourself.
Pinned test cases
Each calculator carries worked examples with expected results, frozen as automated tests. Any change that moves one of those results fails the build.
The point is not to prove the formula is right — a test can only prove it still does what it did. It is to make silent drift impossible: a refactor, a unit change or an overzealous tidy-up cannot quietly alter a published figure.
Confidence, stated on the result
Results carry a confidence level. Arithmetic on measured dimensions is high. An estimate from an empirical relationship with real scatter is medium. A first-order approximation that ignores factors which often dominate in practice is low — and says what it ignores.
A mass-law sound-transmission estimate is a good example: it models a single solid leaf and knows nothing about decoupling, cavity depth or resilient channels, which in a real partition frequently matter more than mass. It is useful for comparing options and useless for certifying a party wall, and the page says exactly that.
A machine check against thin, templated content
Generating many pages from one engine carries an obvious risk: pages that read as variations of each other. Every build measures the similarity of every page against every other page, discounting shared site furniture, and fails if any pair crosses a threshold.
That check has changed the writing more than once. An earlier version of the derived commentary used one fixed sentence structure, and the audit caught hundreds of page pairs that were too alike. The fix was to write better, not to raise the threshold.
What this site is not
It is not an engineer, and it does not know your project. It produces quantities and estimates for planning and ordering. Structural, electrical, gas and life-safety work needs a qualified person and, in most places, the approval of a building authority.
Where a figure could be relied on for something consequential, the page says what it does not cover. Please read those parts — they are the most carefully written text on the site.