Editorial Policy

Sourcing rules

Conversion factors are derived from primary standards bodies wherever one exists: the BIPM SI Brochure and NIST Special Publication 811 for SI-based definitions, national legislation for legally defined units (such as the 1959 international yard and pound agreement or the UK Weights and Measures Act 1985 definition of the imperial gallon), and the current published figure from the relevant body for context-dependent factors such as electricity carbon intensity. Supporting material — history, common mistakes, real-world uses — is checked against these same sources, not written first and matched to a citation afterward. Where a fact cannot be verified against a primary or reputable secondary source, it is left out rather than softened into something vaguer.

Review cadence

Conversion factors fixed by international definition — most of the length, mass, area and volume categories — do not need periodic re-review, because they cannot change. Categories built on a context-dependent, time-varying figure, currently only carbon emissions, are checked whenever the underlying published source updates, at minimum once a year, since bodies such as the IEA and national governments publish updated grid-emissions data annually. Every other page is reviewed when one of the triggers below occurs, rather than on a fixed calendar.

Correction process and turnaround

When an error is reported, the claim is checked against a primary source — a standards body publication, legislation, or, for context-dependent figures, the most recent published data. If the report is correct, the database value and any dependent text are corrected together, so a fix cannot leave the number right and the prose wrong, or vice versa. The site is then rebuilt so the correction is live across every affected page and every supported language, not only the page where the error was reported, and the fix is recorded in the changelog with the date and what changed.

The target is to complete this process, from report to published correction, within 14 days. That is a commitment, not a guarantee — verifying a claim against a primary source can occasionally take longer by itself — but it is the standard this site is held to, and it is stated here rather than left as an unverifiable claim.

What triggers a re-review

• A reader reports a suspected error through the contact page.
• A standards body or government agency publishes an updated figure for a context-dependent value already used on the site, such as an annual grid carbon-intensity update.
• An internal consistency check — the automated test suite that compares every displayed conversion against its stored factor — surfaces a discrepancy during development.
• A unit or category turns out to rest on an assumption that cannot be stated precisely. This is why the heart-rate-variability category was removed rather than corrected: RMSSD and SDNN have no fixed conversion factor between them at all.

Reporting an error

Use the contact page and select “Data correction” as the subject, or write to [email protected] directly. Include the page URL and, if possible, the source you are checking against — that shortens the verification step. Every correction, once verified and published, is added to the changelog.