640 km per hour to mach 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 Mach are 640 Kilometers per Hour we have to multiply 640 by 25 and divide the product by 29817. So for 640 we have: (640 × 25) ÷ 29817 = 16000 ÷ 29817 = 0.53660663379951 Mach
So finally 640 km per hour = 0.53660663379951 mach