Excel: Formulas to Find the Log and Inverse Log of a Number

 Last reviewed: July 15, 1997
Article ID: Q79945

The information in this article applies to:
  • Microsoft Excel for Windows, versions 2.x, 3.0, 4.0, 4.0a, 5.0
  • Microsoft Excel for Windows 95, version 7.0
  • Microsoft Excel 97 for Windows
  • Microsoft Excel for OS/2 versions 2.20, 2.21, 3.0
  • Microsoft Excel for the Macintosh, versions 2.x, 3.0, 4.0, 5.0

SUMMARY

Microsoft Excel has built-in functions to calculate the logarithm of a number with a specified base, the logarithm with base 10, and the natural logarithm. To calculate the inverse log of a number in the first two cases, raise the base to the power of the value returned by the particular logarithm function being used. To find the inverse natural log, use the EXP function.

MORE INFORMATION

You can formulas in the following table to perform logarithmic and inverse log operations. 

   Formula    Operation           Example          Result
   ------------------------------------------------------
   
   =LOG(n,b)  Log base b of n     =LOG(8,2)        3
   =(b)^(x)   Inverse log of the  =2^3             8
              number x, base b
   
   =LOG10(n)  Log base 10 of n    =LOG10(100)      2
   =10^(x)    Inverse log of the  =10^2            100
              number x, base 10
   
   =LN(n)     Natural log of n    =LN(100)         4.6051702
   =EXP(x)    Inverse natural     =EXP(4.6051702)  100
              log of the number x
Note that in the above table, "n" is a variable that is either a value or the address of a cell containing a value, "b" (in the first function) is the base with which the logarithm is calculated, and "x" is a variable representing the result of the log function being used.

Note that unless a different value or cell address is specified, the default value for the base is 10.

REFERENCES

"Microsoft Excel Function Reference," version 3.0, pages 72, 143-144

Additional reference words: 5.00 2.0 2.00 2.01 2.1 2.10 2.2 2.20 2.21 3.0
3.00 4.0 4.00 revlog log10 arc Anti AntiLog anti-log 7.00 8.00

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Last reviewed: July 15, 1997
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