Methodology & Data Sources
Every number on this site is derived from a published standard, not copied from another converter. This page documents exactly how, so you can verify any figure yourself — or cite it.
Primary sources
BIPM — The International System of Units (SI Brochure, 9th edition)
SI base and derived units, prefixes, and the exact defining constants.
NIST Special Publication 811 — Guide for the Use of the SI
Exact US customary ↔ metric factors, rounding and style conventions.
Legal-for-trade weights and measures definitions in the United States.
ISO 80000 — Quantities and units
Quantity naming, symbols, and dimensional consistency.
Astronomical units, light-year, and physical constants.
National statutes, land-revenue codes and standards bodies
Regional and traditional units (tola, bigha, marla, kanal, catty, rai, tsubo, gaj, cent, li). Each carries its own jurisdiction note because these units vary by region and era.
How we compute
Exact factors wherever an exact factor exists
The inch is exactly 25.4 mm, the pound exactly 0.45359237 kg, the US gallon exactly 3.785411784 L. We store the defining exact value and derive everything else from it, rather than chaining approximations.
Conversion happens through a single base unit per category
Every unit in a category declares its ratio to one base unit. A conversion is therefore two operations, not a lookup in a hand-maintained matrix — which removes the possibility of one pair disagreeing with another.
Non-linear scales are formulas, not factors
Temperature, fuel economy, and similar scales use an offset or reciprocal relationship. Those pages state the formula instead of a misleading single multiplier.
Rounding is display-only
All arithmetic runs at full double precision. The decimal-precision selector changes only what is shown, never what is computed, so chained conversions do not accumulate rounding error.
Ambiguous units are disambiguated, not silently guessed
A "ton", a "gallon", a "bigha" and a "mile" all mean different things in different places. Where a name is ambiguous we ask which one you mean and label the variant on the result.
Corrections are welcome and public
If a figure here disagrees with a primary source, tell us and we will correct it and note the change. Accuracy claims are worthless without a correction path, so every change to a published number is logged with its date and cause on our corrections page.
Review cadence
Standards-derived factors are fixed by definition and change only when a standards body redefines them. Regional and traditional units are reviewed quarterly against the relevant statute or land-revenue code, because these genuinely do change. Currency rates are the only live data on the site and are labelled with their retrieval time.
What “verified” means here
466 units across 36 categories are each traced to one of 15 primary sources. Every page carries the date below, so you never have to guess how current a figure is.
1. Defined against a primary standard
Every unit resolves to an SI base unit through a factor traced to BIPM, NIST, ISO 80000 or the governing national statute, recorded per unit in the provenance dataset.
2. Exactness is labelled, not assumed
Each factor is classified as exact by definition, exact by convention, measured, or regionally variable — so a rounded or disputed value is never presented as definitive.
3. Rebuilt and re-audited on every change
Continuous integration re-runs the structural SEO audit, accessibility checks and Lighthouse budgets across the prerendered pages before anything ships.
4. Corrections are public and welcomed
Reported errors are fixed at the data layer, which updates every page that depends on the figure in one pass, and each change to a published number is recorded with its date and cause in the public corrections log at /corrections.
Who is accountable
The maintainers responsible for sourcing, verifying and correcting every published figure on UnitConvertLab. We do not publish invented expert bylines: until an individual specialist signs off on a dataset, accountability sits with the organisation as a whole, and the process above is what you should judge us on. We take no payment for placement, run no sponsored conversion content, and require no account to use anything on the site.
Content last rebuilt and audited ; source data last reviewed .
Every change to a published figure is recorded in the public corrections log, with the date, the cause, and how the error was found.
Cite this page
UnitConvertLab. (2026). Methodology & Data Sources. UnitConvertLab. Retrieved from https://unitconvertlab.com/methodology
Found an error? Report it and we will correct it, then log the change at /corrections.