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Excel LOG Function

The LOG function returns the logarithm of a number, using a specified base.

log function 1


=LOG (number, [base])


  • Number (required): The positive number that you want to calculate the logarithm of.
  • Base (optional): The base of the logarithm. If omitted, it defaults to 10.

Return value

The LOG function returns a numeric value.

Function notes

  1. Both arguments in the LOG function should be supplied as positive numeric values.
  2. LOG function will return the #VALUE! error if any of the supplied arguments are non-numeric.
  3. LOG function will return the #NUM! error if:
    • number ≤ 0
    • base≤ 0
  4. LOG function will return the #DIV/0! error if base equals 1.


To get the logarithms of numbers to specified bases in the below table, please copy the formulas below into cell E4, E5, E6 and E7 respectively and press the Enter key to get the results.

=LOG (B4)

=LOG (B5, C5)

=LOG (B6, C6)

=LOG (B7, C7)

log function 2


  1. In the formula of Cell E4, the base argument is omitted and defaults to 10.
  2. We can directly input the values of the two arguments in the formula. The four formulas above can be changed to:

    =LOG (10)

    =LOG (8, 2)

    =LOG (16, 3)

    =LOG (88, 3.5)

Relative Functions:

  • Excel EVEN Function
    The EVEN function rounds numbers away from zero to the nearest even integer.

  • Excel EXP Function
    The EXP function returns the result of the constant e raised to the nth power.

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