To convert any other number system to decimal, write the number in expanded form and evaluate using the decimal number system.

__Example__1265 in octal is 1*8^3 + 2*8^2 + 6*8^1 + 5*8^0 = 1*512 + 2*64 + 6*8 + 5 = 512 + 128 + 48 + 5 = 693 in decimal