Editorial and accuracy policy

Convertly publishes reference material that people use to make real decisions — dosing, machining tolerances, freight weights, oven temperatures. This page explains where the numbers come from, who writes the guidance around them, and what happens when something is wrong.

Where the factors come from

Every conversion factor on the site is entered from a primary standards document, not copied from another converter. Each unit stores its exact relationship to the SI base unit for its category, together with a flag recording whether that relationship is exact by definition or a measured value.

• NIST Special Publication 811US guide for the use of the SI, including the conversion factors between US customary and metric units.
• BIPM — The International System of Units (SI Brochure)Definitive definitions of the SI base and derived units.
• NIST Handbook 44Legal metrology definitions used in US trade, including the survey foot and commercial weights.
• UK Weights and Measures Act 1985Statutory definitions of Imperial units still in legal use in the United Kingdom.
• IEC 80000-13Binary prefixes (kibi, mebi, gibi) that separate 1,024-based units from decimal SI units.

How the maths is done

A conversion goes from the input unit to the category base unit and back out to the target unit, entirely in IEEE-754 double precision. Nothing is rounded in between, so chained or repeated conversions do not accumulate error. Rounding happens once, at display time, and the page tells you when the underlying factor is exact and only the display is rounded.

Regional units are never merged

US customary and Imperial measures share names but not sizes. Gallons, pints, fluid ounces and tons are stored as separate units, and any page that touches them states which system it is using. We would rather add a sentence than quietly introduce a 20% error.

Who writes the guidance

The explanatory sections — worked examples, mental shortcuts, common mistakes, precision advice and the long-form guides in Learn — are written and edited in-house by the Convertly editorial team, then checked against the sources above before publication. Guides carry a last-updated date, and we revise them when a standard changes or a reader reports a problem.

Corrections

If a factor, formula or explanation looks wrong, report it through the contact page. Accuracy reports are handled ahead of everything else; confirmed errors are fixed site-wide, because every page derives from the same unit definitions.

Advertising and independence

Convertly is free to use and supported by advertising. Advertisers have no influence over the conversion factors, the guidance or which pages exist, and no advertisement is ever presented as editorial content.