The Logarithm of a number, to a given base, is the power to which the base must be raised to give that number.
The Base 10 Logarithm of a number, (also known as the Common Logarithm and written as Log_{10}(x) ), is the logarithm to the base 10.
Therefore,
The Excel LOG10 function calculates the base 10 logarithm of a given number.
The syntax of the function is:
where the number argument is the positive real number that you want to calculate the base 10 logarithm of.
The following spreadsheet provides four examples of the Excel Log10 function:
Formulas:
 Results:

For further examples of the Excel Log10 function, see the Microsoft Office website.
If you get an error from the Excel Log10 function, this is likely to be one of the following:
#NUM!    Occurs if the supplied number argument is negative or zero. 
#VALUE!    Occurs if the supplied number argument is nonnumeric. 