Often, it is necessary to output numbers, but you may want to control the number of digits and would like to control the formatting. The -f operator can do this and has a trillion options but there's just one you need to remember: N0 (the "0" is the number zero).
PS> '{0:N0}' -f (8GB/12KB) 699,051
It rounds the number so there are no digits after the decimal, and it adds a separator every three numbers if the number is more than 999. Replace "N0" with "N1" or any other number to control the digits after the decimal:
PS> '{0:N2}' -f (8GB/12KB) 699,050.67