The Excel Oct2Dec function converts an Octal (a base8 number) into a decimal number.
The syntax of the function is:
Where the number argument is the octal number that is to be converted to a decimal.
Note that the supplied number argument must not be more than 10 characters (40 bits) long. The most significant bit of this value denotes the sign of the number and the remaining 39 bits denote the magnitude. Negative numbers are represented using two's complement notation.
The Octal (Base 8) Numeral System uses the digits 07.
The following table shows the first 16 octal values, along with the equivalent decimal values:
Octal  1  2  3  4  5  6  7  10  11  12  13  14  15  16  17  20 
Decimal  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16 
The following spreadsheets show five examples of the Excel Oct2Dec function.
Formulas:

Results:

Note that, in the above example spreadsheet, the negative octal in cell A4 is represented by two's complement notation.
Further details and examples of the Excel Oct2Dec function are provided on the Microsoft Office website.
If you get an error from the Excel Oct2Dec function this is likely to be the #NUM! error:
#NUM!    Occurs if the supplied number argument is not recognised as a octal number, or contains more than 10 characters. 