You are converting to octal so each position is a power of 8 so 264 is 2X64+6+64+4 becasue of the numbering systems you can do this by counting off units of 3 from the right and converting to decimal and as the largest 3 digit binary number 111=7 this converts directly into octal.

so 001000 =10 in octal = 8 in decimal
001111 =17 in octal = 15 in decimal
010000 =20 in octal = 16 in decimal
etc
111000 =70 in octal = 48 in decimal