LOG Function in Excel (Table of Contents)
LOG in Excel
The LOG function is a worksheet function categorized under Math/Trigonometry function.
As per the Mathematics, the logarithm is defined as an inverse function to exponentiation or logarithm of a positive real number x with respect to base b. i.e. b^{x}=y
E.G. log_{2} 16 = 4, since 2^{4} = 2 ×2 × 2 × 2 = 16
Here, the logarithm (with respect to base 2) of 16 is 4.
The LOG function in Excel is easy to use & very simple, it is most widely used function in statistics, finance & business analytics field or domain.
The LOG function is also used to plot a graph for data representation & it is used with other tools for regression analysis.
The LOG function performs the inverse operation to that of a POWER function.
LOG function in excel calculates the logarithm of a given number, to a supplied base or it returns the natural logarithm of a number.
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E.G. 1000 = 10 × 10 × 10 = 10^{3}, the “logarithm to base 10” of 1000 is 3 i.e. logarithm counts repeated multiplication of the same factor. The logarithm of a given number x is the exponent to a fixed number, the base b, must be raised, to produce that number x.
i.e. If a^{x} = b Then Log_{a}(b) = x.
LOG Formula in Excel
Below is the LOG Formula in Excel :
or
Explanation of LOG Function in Excel
LOG formula in Excel consists of two things Number & Base.
 Number = It is a positive real number that you want to calculate the logarithm in excel.
Note: It should be a numeric value that must be always greater than zero.
 Base = It is a base to which the logarithm should be calculated or It is an optional argument that specifies or indicates the base to which the logarithm should be calculated.
Note: If no base is listed, the base is assumed to be 10.
How to Use the LOG Function in Excel?
The LOG function in Excel is very simple and easy to use. Let understand the working of LOG function in Excel by some LOG Formula example.
Example #1 – With Base Argument
In the belowmentioned example, let’s calculate the logarithm in excel of 47, with base value 10.
Follow these steps to calculate the LOG in Excel:
 Select the output cell where we need to find out log value i.e. D8 in this example.
 Click the function button (fx) under formula toolbar, a popup will appear, under the select function, doubleclick on LOG function.
 A dialog box appears where arguments (Number & Base) for log function needs to be filled.
 Here the number is 47 & base argument is 10.
 Excel calculates the logarithm value and displays the answer 1.6720979 in the output cell.
Example #2 – Without Base Argument
In the belowmentioned example, let’s calculate the logarithm of 100, without base value.
Follow these steps to calculate the LOG in Excel:
 Select the output cell where we need to find out log value i.e. D13 in this example.
 Click the function button (fx) under formula toolbar, a popup will appear, under the select function, doubleclick on LOG function.
 A dialog box appears where arguments (Number & Base) for log function needs to be filled.
 Here the number is 100 & In this log function example, Log function by default takes the base value as 10 if the second argument (Base) is not passed in log function.
 Excel calculates the logarithm value and displays the answer 2 in the output cell. i.e. 100 = 10 × 10 = 10^{2}, the “logarithm to base 10” of 100 is 2 i.e. logarithm counts repeated multiplication of the same factor. Therefore, it returns the output value or a result as 2.
Example #3 – With Decimal Value As Base Argument
In the belowmentioned example, let’s calculate the logarithm of 6, with decimal value 0.5 as the base argument.
Follow these steps to calculate the LOG in Excel:
 Select the output cell where we need to find out log value i.e. D17 in this example.
 Click the function button (fx) under formula toolbar, a popup will appear, under the select function, doubleclick on LOG function.
 A dialog box appears where arguments (Number & Base) for log function needs to be filled.
 Here the number is 6 & base argument is 0.5.
 Excel calculates the logarithm value and displays the answer 2.584963 in the output cell. i.e. 0.5^{2} = 6; Therefore, Log_{0.5}(6) = 2.584963
Example #4 – When Base Argument is Negative Value or Zero
In the belowmentioned example, let’s calculate the logarithm in excel of 47, with base argument “0” ZERO or Negative value (10).
Follow these steps to calculate the LOG in Excel:
 Select the output cell where we need to find out log value i.e. K8 in this example.
 Click the function button (fx) under formula toolbar, a popup will appear, under the select function, doubleclick on LOG function.
 A dialog box appears where arguments (Number & Base) for log function needs to be filled.
 Here the number is 47 & base argument is 1.
or 0.
 Let’s calculate the logarithm in excel value and display the answer #NUM! error in the output cell.
Example #5 – When Base Argument is NonNumeric Or Text Value
In the belowmentioned example, let’s calculate the logarithm of 47, where the base argument is text string i.e. “EXCEL”.
Follow these steps to calculate the LOG in Excel:
 Select the output cell where we need to find out log value i.e. K16 in this example.
 Click the function button (fx) under formula toolbar, a popup will appear, under the select function, doubleclick on LOG function.
 A dialog box appears where arguments (Number & Base) for log function needs to be filled.
 Here the number is 47 & base argument is TEXT string i.e. EXCEL.
 Excel calculates the logarithm value and displays the answer #VALUE! error in the output cell.
Things to remember about the LOG Function in Excel
 Number argument in LOG Function: It should be always a positive real number that you want to calculate the logarithm in excel.
 It should be numeric value & must be always greater than zero.
 In Base argument, if no base is listed, the base is always assumed to be 10.
LOG Function Errors
If there is an error from the Log function, it is due to one of the following:
Common Errors
1) #VALUE! – It Occurs due to or if supplied number argument or the supplied [base] argument is nonnumeric.
2) #NUM! – It Occurs due to or if the supplied number argument or the supplied [base] argument is the negative value or zero.
The output will be :
3) #DIV/0! – It Occurs if the supplied [base] argument is equal to 1.
The output will be :
You can download this LOG Function Excel Template here – LOG Function Excel Template
Recommended Articles
This has been a guide to the LOG in Excel. Here we discuss the LOG Formula in Excel and How to use LOG Function in Excel along with practical examples and downloadable excel template. You can also go through our other suggested articles –
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