Example A: 5.5 km × 0.621371192 = 3.4176 mi (precision = 4).
Example B: 250.8 km × 0.621371192 = 155.846 mi (precision = 3).
Quick-Facts
Exact factor: 1 km = 0.621371192 mi (NIST SP 811, 2008).
Kilometre derives from the SI base unit metre (BIPM SI Brochure 9th ed., 2019).
USA and UK road signs display miles; 95 % of countries use kilometres (UK DfT Sign Manual 2022).
“NASA calculates in metric, then converts for the public” (NASA Metric Transition Policy 2007).
FAQ
What is a kilometre?
It is 1,000 metres, the standard SI multiple for long distances (BIPM SI Brochure 2019).
Why does the tool use 0.621371192 as the factor?
NIST lists this as the exact survey conversion between kilometres and international miles (NIST SP 811 2008).
Can I convert miles back to kilometres?
Yes—invert the factor: $$\text{Kilometres}= \text{Miles} ⁄ 0.621371192$$ (NIST, 2008).
How accurate are six decimal places?
Six decimals keep error below 0.001 m per kilometre—adequate for mapping (USGS Geodesy Factsheet 2021).
Why do U.S. runners track miles?
Imperial units persist in U.S. athletics regulations (USA Track & Field Rule Book 2023).
Is the factor affected by altitude?
No—conversion is purely numeric; altitude influences only physical travel, not units (NIST, 2008).
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