How do you compute octal number to decimal number?

Answer 1

In decimal numbers each digit to the left of the decimal point represents the number of lots of 10^0 (units), 10^1 (tens), 10^2 (hundreds), and so on. To the right they are lots of 10^-1 (tenths), 10^-2 (hundredths) and so on. The pattern is the same with octal numbers except that the 10 are replaced by 8.

So, starting with the "octal point", which would be equivalent to a decimal point, the digit immediately to the left represents the number of 8^0 (=1). The digit to the left of that represents the number of lots of 8^1 (=8). To the left of that is the number of 8^2 (=64) and so on. To the right of the point it is the number of 8^-1 (=1/8), then 8^-2 (=1/64) and so on.

So for example, Octal(3647.2) = 3*8^3 + 6*8^2 + 4*8^1 + 7*8^0 + 2*8^-1 in decimal

= 3*512 + 6*64 + 4*8 + 7*1 + 2*1/8

= 1536 + 384 + 48 + 7 + 0.25 = 1959.25