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

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Article ID: 214116 - View products that this article applies to.
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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 use the 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
				
In the preceding 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: Unless a different value or cell address is specified, the default value for the base is 10.

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Article ID: 214116 - Last Review: September 18, 2011 - Revision: 4.0
APPLIES TO
  • Microsoft Excel 2000 Standard Edition
  • Microsoft Excel 2002 Standard Edition
  • Microsoft Excel 97 Standard Edition
  • Microsoft Excel 2001 for Mac
  • Microsoft Excel 98 for Macintosh
  • Microsoft Office Excel 2003
  • Microsoft Excel 2010
  • Microsoft Office Excel 2007
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