Exact constants

Values defined by international agreement, such as metric prefixes and SI unit relationships, are treated as exact. Conversions between exact units carry no intrinsic error beyond the rounding applied for display.

Approximate constants

Values based on measurement, convention, or regional standards are approximate. Examples include historical definitions, cooking conversions, and certain regional weights and volumes. The interface notes when a conversion relies on an approximate factor.

Floating-point limits

All calculations use JavaScript's double-precision floating-point numbers. This is more than enough for everyday conversions, but very large or very small values may show tiny representation errors in the least significant digits.

Known limitations

Time-zone calculations depend on the accuracy of the browser's time-zone data and the selected date. Future dates beyond the current IANA release may not reflect future rule changes. Projections, such as running race estimates, are intended as guidance rather than guarantees.