Conversion Methodology
This page explains exactly how Convert Calc turns a value in one unit into a value in another — where the underlying factors come from, how results are rounded, and how we keep that information accurate over time. We publish this so anyone can verify our numbers independently rather than taking them on faith.
How conversions are calculated
For most categories — length, weight, volume, area, speed, time, pressure, energy,
power, data storage, frequency, force, angle, and typography — every unit is defined
by a single toBase factor relative
to a fixed reference unit for that category (for example, the meter for length or the
kilogram for weight). Converting from one unit to another is:
result = (value × from.toBase) / to.toBase
This base-unit approach means we don't maintain a separate factor for every possible pair — a single, independently verifiable number per unit covers all conversions in that category, which keeps the numbers small, auditable, and consistent.
Temperature doesn't fit this model because Celsius, Fahrenheit, and Kelvin scales don't share a common zero point, so Convert Calc applies the standard affine formulas (e.g. °F = °C × 9/5 + 32) directly rather than forcing them through a base-unit factor.
Fuel economy is an inverse relationship — lower L/100km is more efficient, while higher MPG is more efficient — so every fuel economy conversion routes through liters-per-100km as an intermediate step rather than a direct multiplication.
Sources
Conversion factors are drawn from published standards, primarily NIST SP 811 (Guide for the Use of the International System of Units), the SI Brochure (BIPM), and IEC 80000 for binary data prefixes. Each converter page cites the specific source used for that factor in its Formula section.
Rounding and precision
The live converter widget displays results to a fixed number of decimal places chosen per category to balance readability with precision (for example, 4 decimal places for length, fewer for large units like data storage). Conversion tables and worked examples on each page show pre-computed values rounded the same way. If you need full floating-point precision for a calculation, use the underlying factor shown in the Formula section directly.
Review cadence
Converter pages with rich content display a "Last reviewed" date — the date the conversion factor, formula, and examples on that page were last checked against the cited source. Conversion factors for standardized units essentially never change, but we periodically re-review pages to fix wording issues, broken links, and outdated examples.
If you spot an error or an outdated example, let us know — every report is checked against the primary source before any correction is made.