Converting between metric and imperial length
Length is one of the most commonly converted measurements, mostly because the world runs on two different systems at once: metric (millimetres through kilometres), used by nearly every country, and imperial (inches through miles), still used for everyday measurement primarily in the United States, with partial use in the UK and a few other countries.
All conversions here run through metres as a common base unit — converting any unit to metres, then from metres to the target unit — which keeps the underlying math simple and consistent regardless of which two units you're converting between.