Compute the decimal equivalent of each integral octal digit. Multiply each digit by 8 raised to the power of the digit's relative position, starting with zero. For example, the decimal equivalents of the digits 1, 2 and 4 in the octal number 124.45 are 64 (1 x 8^2), 16 (2 x 8^1) and 4 (4 x 8^0).
Calculate the decimal equivalent of each fractional octal digit. Divide each octal digit by 8 raised to the power of the digit's relative position, starting with 1. Continuing with the example, the decimal equivalents of the digits 4 and 5 in the octal number 124.45 are 0.5 [4 / (8^1) = 4 / 8 = 0.5] and 0.078125 [5 / (8^2) = 5 / 64 = 0.078125].
Convert an octal number to decimal. Add the decimal equivalents of the integral and fractional octal components separately, and then add them together. To conclude the example, the decimal equivalents for 124 octal and 0.45 octal are 84 (64 + 16 + 4) and 0.578125 (0.5 + 0.078125). The 124.45 octal is 84.578125 in decimal.