Methodology
This page documents how every number on Convertitive is calculated. Showing the work matters: a conversion site that can’t be audited is just a guess with confidence.
Data sources
- SI units are defined per the BIPM SI Brochure, 9th edition (2019 redefinition), which fixes the values of Planck’s constant, the elementary charge, Boltzmann’s constant, and Avogadro’s constant exactly.
- Imperial / US customary units are derived from the 1959 international yard and pound agreement: 1 in = 25.4 mm and 1 lb = 0.45359237 kg, both exact.
- Practical conversion factors (where calculations require a stored ratio) are cross-checked against NIST Special Publication 811.
- Astronomical units (light year, parsec) follow the IAU 2012 / 2015 resolutions and use the Julian year (365.25 d).
How conversion works
Every unit is stored with a pair of numbers: factor and offset. To convert a value v from unit A to unit B:
base = v × A.factor + A.offset result = (base − B.offset) / B.factor
For ratio-only categories (length, weight, volume, speed, time), every offset is zero and the formula collapses to v × A.factor / B.factor. For temperature, where the scales have different zero points, the offset carries that information.
Precision and rounding
All arithmetic uses IEEE 754 double-precision floating point — the JavaScript Number type — which is accurate to roughly 15–17 significant digits. Identity conversions (e.g. 5 cm → 5 cm) are short-circuited to avoid floating-point noise. Displayed results are formatted to six significant digits by default, with very large or very small magnitudes switched to scientific notation.
Corrections
If you spot a wrong number, please email hello@convertitive.com with the page URL and your reasoning. We’ll publish a fix within one business day and credit reporters on this page on request.