Length Converter
mm to nautical miles, with the PCB designer's mil in between.
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The engineering
Machining and PCB work live on the inch and its thousandth (the mil, or 'thou' — 25.4 µm), fabrication drawings mix mm and inches on the same sheet, aviation and marine navigation run nautical miles (one arcminute of latitude, 1852 m), and everything scientific runs metric. The 1959 agreement made the inch exactly 25.4 mm, so inch↔mm conversions are exact and the only rounding is yours.
The classic mistakes: reading 'mil' as millimeter (a 10 mil trace is 0.254 mm — order one at 10 mm and you've made a bus bar), mixing drawing units on dual-dimensioned prints, and the pre-2023 US survey-foot vs international-foot gap (2 ppm — invisible on a bracket, a few feet across a state plane coordinate system, which is why NIST finally killed the survey foot).
Where this math comes from
The metre is French Revolution engineering: defined in 1793 as one ten-millionth of the pole-to-equator quarter meridian, surveyed by Delambre and Méchain through seven years of war and triangulation, and cast as the platinum Mètre des Archives in 1799. The 1875 Metre Convention internationalized it; in 1983 the CGPM re-anchored it to the speed of light, making the metre a property of physics rather than a bar in a vault.
America's inches have been metric underneath for longer than most people think: the 1893 Mendenhall Order defined US customary length from the meter, and the 1959 international yard-and-pound agreement fixed the yard at 0.9144 m exactly — making 25.4 mm/in exact and ending centuries of slightly-different inches. The nautical mile went international at 1852 m in 1929 (Monaco Hydrographic Conference), keeping one unit tied to the geometry of the globe itself.
- 1793French Republic (Delambre & Méchain survey)Metre defined from the Earth's meridian.
- 1799French AcademyPlatinum Mètre des Archives deposited.
- 1893T. C. MendenhallUS customary units legally defined from the meter.
- 1959Six-nation agreementInternational yard: 1 in = 25.4 mm exactly.
- 198317th CGPMMetre redefined via the speed of light.
See the full timeline of the math behind every calculator →
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