21 km to mi conversion result above is displayed in three different forms: as a decimal (which could be rounded), in scientific notation (scientific form, standard index form or standard form in the United Kingdom) and as a fraction (exact result). Every display form has its own advantages and in different situations particular form is more convenient than another. For example usage of scientific notation when working with big numbers is recommended due to easier reading and comprehension. Usage of fractions is recommended when more precision is needed.
If we want to calculate how many Miles are 21 Kilometers we have to multiply 21 by 15625 and divide the product by 25146. So for 21 we have: (21 × 15625) ÷ 25146 = 328125 ÷ 25146 = 13.048795036984 Miles
So finally 21 km = 13.048795036984 mi
