Km to Miles Converter

The exact relation 1 international mile = 1609.344 m derives from the 1959 International Yard and Pound Agreement, which fixed the yard at exactly 0.9144 m. A statute mile is 5,280 feet = 1,760 yards = 63,360 inches; multiplying 1,760 × 0.9144 yields 1609.344 m exactly. Six English-speaking nations — the United States, United Kingdom, Australia, Canada, New Zealand, and South Africa — adopted this single international mile to replace their slightly different historical miles. The U.S. National Bureau of Standards published the agreement in the Federal Register on 30 June 1959 (Doc 59-5442), effective 1 July 1959. The reciprocal 1 km = 1000/1609.344 mi = 0.62137119223733… mi expands non-terminating in decimal but is exact in rational form.

Before 1959, the United States used a slightly different foot — the U.S. survey foot, defined by the 1893 Mendenhall Order as exactly 1200/3937 m ≈ 0.30480061 m. After 1959, the international foot of exactly 0.3048 m was adopted for general use, but the survey foot was retained for land surveying and the State Plane Coordinate Systems (SPCS) of 1927 and 1983 to avoid disrupting decades of geodetic data. The two definitions differ by about 2 parts per million — small for a single measurement but accumulating over the kilometre-long distances common in surveying. NIST and NOAA jointly deprecated the U.S. survey foot effective 31 December 2022 (Federal Register notice 5 October 2020); the international foot now applies for all new surveying work, and NGS continues legacy support for SPCS 1983 and 1927.

The international statute mile (this page's unit) is exactly 1609.344 m. A nautical mile is exactly 1852 m by international agreement (the First International Extraordinary Hydrographic Conference convened by the International Hydrographic Bureau in Monaco, 1929) — it approximates one minute of arc along a meridian, the historical motivation for the unit, so it is the natural unit for marine and aviation navigation. A 'metric mile' is an informal name for several distances depending on context: 1500 m in athletic events (the Olympic 'metric mile'), 1600 m in U.S. school track meets, or sometimes literally 1 km in casual usage. When a distance is stated without qualification, 'mile' in the United States, United Kingdom, and most former British territories means the statute mile.

Resolution 1 of the 17th CGPM (October 1983) redefined the metre as the length of the path light travels in vacuum during 1/299,792,458 of a second — fixing the speed of light c at exactly 299,792,458 m·s⁻¹. Before 1983, the metre was defined by a specific number of wavelengths of krypton-86 radiation; before 1960, by a platinum-iridium bar at the BIPM (the 1889 international prototype metre). The 1983 redefinition tied the metre to a fundamental physical constant rather than a material artifact, the same shift that came to the kilogram in 2019 via the Planck constant. Because c is now an exact defined value, the metre and every length unit derived from it (yard, foot, mile) are pegged to the second — itself defined since 1967 by caesium-133 atomic transition frequency.

The miles result and the swap-button label sit inside an aria-live="polite" region — the W3C WCAG Success Criterion 4.1.3 (Status Messages, introduced in WCAG 2.1, Recommendation 5 June 2018; carried unchanged into WCAG 2.2, Recommendation 5 October 2023) pattern. Polite live regions queue announcements after any speech in progress, so updating the kilometres input announces the new miles value without interrupting the user mid-sentence. Screen readers (NVDA, JAWS, VoiceOver) consume the live region automatically; the user does not need to do anything else.