Units of measurement
The International System of Units (SI) is now the most widely used system of measurement. The SI defines base units that include second for time, metre (meter) for length and kilogram for mass. However, the United States customary units (for example, inch, foot, yard, and mile for length, degrees Fahrenheit for temperature) are in common use in the United States. The comparable imperial system of units is still in common use in parallel with the SI system in several countries/regions; for example, to measure distance in the UK. There are differences between United States customary units and the imperial system of units; for example, the United States fluid gallon is smaller than the imperial fluid gallon.
When converting measurements between two different systems of units, it's important to ensure that you know both systems of measurement in use, especially if the unit of measurement is ambiguous. For example, a fluid ounce could be either a United States fluid ounce or an imperial fluid ounce. Programming languages and frameworks don't usually provide conversions between SI/metric units and United States or imperial units, or between United States units and imperial units. You might be able to use a published library for these types of conversions.
Similarly, your programming language or framework might provide methods to determine whether the locale uses the SI (metric) system or another measurement system. These methods don't handle the case where the national standard is one system, but different units of measurement are used in specific cases.