Calculation model
Linear units convert through one reference value: input is transformed to the category reference, then transformed into the output unit. Temperature also applies offsets. Frequency-to-wavelength pages use the inverse relationship with the exact speed of light in vacuum.
Calculators keep full JavaScript double precision until display. Number-base conversion uses integers and rational fractions built with BigInt, so long integer inputs do not pass through floating-point numbers.
Exact and approximate values
Definitions marked exact include SI prefix powers, the international inch and pound, standard gravity, the speed of light, the elementary charge, and legal gallon definitions. Decimal output can still repeat, so the interface rounds presentation without changing the stored conversion factor.
Context-dependent conversions carry their assumption beside the result. Examples include CSS pixels at 96 PPI, electromagnetic wavelength in vacuum, and ingredient density for cup-to-gram estimates.
Review tiers
Core converters use factors reviewed directly against the authority linked on the category page. Extended engineering categories preserve ConvertWin's established factor inventory so discontinued technical pages remain useful; their pages label that status and separate the cited SI framework from conventional or domain-specific factors.
Extended factors pass structural, finite-value, reciprocal-route, and representative calculation tests. They are suitable for general calculation and discovery, but safety-critical, regulated, or contractual work must be checked against the governing domain standard.
Primary references
| Authority | Used for |
|---|---|
| BIPM SI Brochure | SI base and derived units, constants, and prefixes |
| NIST Special Publication 811 | SI usage and accepted non-SI relationships |
| IEC binary prefixes | KiB, MiB, GiB, TiB, and binary multiples |
| W3C CSS Values and Units | CSS reference pixel and absolute web lengths |
| IANA Time Zone Database | City time-zone identifiers and civil-time rules |
| W3C WCAG 2.2 | Color contrast calculation and thresholds |
Review and correction policy
High-use and standards-sensitive categories are reviewed first. A change to a constant requires a source, an automated test, and a review of every generated page that uses it. Content pages show their category source and accuracy note so assumptions are not hidden in a global disclaimer.
Last reviewed: July 29, 2026.