How we calculate
Two kinds of number appear on this site, and they deserve different amounts of trust.
Geometry is exact
Areas and volumes are arithmetic. A rectangular slab is length times width times thickness; a cylinder is its cross-section times its height. There is no judgement in these steps and no source to cite, which is why every calculator shows its formula: you can check the result by hand.
Unit conversions are also exact. An inch is defined as 25.4 millimetres, a foot as 0.3048 metres, a pound as 0.45359237 kilograms. These are definitions rather than measurements, so we use them at full precision and never round the factors themselves.
Material figures are not exact
How much a cubic yard of gravel weighs depends on the rock, the gradation and how wet it is. How much concrete comes out of a bag depends on the product. How much a compacted base settles depends on the material and the effort put into compacting it. Anyone quoting one of these to four significant figures is inventing precision.
So we do three things instead. We show a range where the value genuinely varies. We list the figure we used, in public, on the page that used it. And we say whether anyone has actually checked that figure against the source we cite.
What "verified" means here
Verified means a person opened the cited document and confirmed the number. Not yet verified means we have identified the right authority but have not done that check, so the figure is a working placeholder.
A calculator page is not allowed to be published to search engines while it still depends on an unverified figure. That rule is enforced by the build, not by good intentions. The validator fails if a page marked indexable relies on an assumption that has not been checked.
Registry state right now: 2 of 18 assumptions verified, 16 still awaiting review, across 13 registered sources.
What this site will not do
- Quote live material prices. Prices move locally and constantly; you enter your own.
- Tell you how thick a slab should be, or what reinforcement it needs. That is design.
- Present an estimate as a specification, or as a code-compliance determination.
- Pass your measurements to anyone. Nothing you type here leaves your browser.