Methodology
How a tool gets onto this site, and what is checked before it does.
One question per tool
Each page answers a single question that ends in a number, and contains its own arithmetic. No page is a rewrite of another; near-duplicate variants are consolidated into one page that handles both phrasings.
Formula stated, always
The formula is written out in words and, where it is not obvious, in symbols. Any constant that comes from outside — a coverage rate, a bag yield, a density — names its source and its typical range, because those constants are where most calculators go wrong.
Testing before publication
Every tool ships with at least three test cases, including a boundary case, checked against a hand calculation. The test suite runs as part of the publish process: a tool that fails a test does not go live.
Assumptions and limits
Where a result is only valid for a range of inputs, the page says so. Where a result is inherently approximate, the page says that too. Silent limitations are treated as defects.
Corrections
Reported errors are verified against the formula and the source, fixed, re-tested, and the page's update date changes. If a report shows the underlying assumption was wrong rather than the arithmetic, the assumption is rewritten and the change noted.