This page explains where Convertly’s conversion relationships come from, how the calculators handle precision, and how we review corrections. The goal is to make every result understandable and reproducible—not merely to display a number.
Our source hierarchy
We prefer primary, standards-based references. For SI units and accepted non-SI units, we use the International Bureau of Weights and Measures (BIPM) SI Brochure. For U.S. customary usage and practical conversion guidance, we consult the National Institute of Standards and Technology (NIST), including Handbook 44, Handbook 130, and NIST Special Publication 811 where relevant. Exact internationally agreed relationships—such as one inch equaling exactly 2.54 centimeters—are stored as exact definitions rather than rounded estimates.
When a term can have more than one meaning, the calculator must identify the convention it uses. Examples include U.S. versus imperial gallons, short tons versus long tons and metric tonnes, and decimal versus binary digital-storage prefixes. We do not silently combine incompatible systems.
How a calculator works
Each page states a relationship between an input unit and an output unit. For a scale conversion, the entered value is multiplied by a factor or divided by its reciprocal. Temperature conversions use both a scale and an offset, so they are calculated with the complete formula rather than a single factor. The arithmetic runs in the visitor’s browser. Values entered into the calculator are not submitted to Convertly.
The displayed reference table and worked example are generated from the same underlying relationship used by the interactive calculator. This gives readers three ways to check a result: use the calculator, follow the stated formula manually, or compare against a known table value.
Precision and rounding
A long decimal is not automatically a more accurate measurement. Convertly retains additional digits during the calculation and rounds the displayed answer for readability. The appropriate final precision depends on the original measurement and its purpose. If a length was measured only to the nearest centimeter, reporting the converted result to ten decimal places would imply accuracy the measurement never had.
For everyday estimates, two to four significant figures are often adequate. Engineering, laboratory, surveying, financial, medical, and regulated uses may require a documented rounding rule or calibrated equipment. In those settings, treat Convertly as an arithmetic aid and follow the standard or procedure governing the work.
Important limitations
- A unit conversion changes the unit, not the quality of the original measurement.
- Volume-to-mass cooking conversions require ingredient density and cannot be inferred from volume alone.
- Pressure readings may be gauge or absolute; a numeric conversion does not reconcile those reference points.
- Calendar durations depend on dates, leap years, and time zones and are not the same as fixed elapsed-time conversions.
- Property, safety, health, tax, and commercial decisions can be governed by local definitions or regulations.
Editorial review and corrections
New converters are checked for unit identity, direction of conversion, factor or formula, example output, labels, and mobile usability. When a correction is made, we update the affected formula, examples, table, metadata, and structured information together so that the page does not give conflicting answers.
If you believe a result is wrong, use the contact page and include the page address, the value entered, the result shown, the expected result, and the source you used. We review reproducible reports and correct verified errors. Material content is reviewed when standards change or when a reported issue identifies an ambiguity.