How to Plot Logarithmic Functions in Excel

Microsoft Excel is used by many people to store information and create charts, but it can also be used to graph functions. Log functions are no exception. By using a combination of Excel's "LOG()" function and the regression tool you can create a smooth looking log graph. With a basic understanding of Excel the process only takes a few minutes.

Two Men Using Tablet, Asian Mix Race Friends Guys
credit: gmast3r/iStock/Getty Images

Step

Enter a series of values in column "A" that correspond to the x-axis markers you want to use. For example if your data runs from 0-100, you might choose to enter the "x" values 10, 20, 30, etc. Just make sure that your "x" values are spread out and not bunched closely together.

Step

Enter "=LOG(A1,[base])" in cell B1, replacing [base] with the logarithmic base number your function uses. Most log functions use base 10. Alternatively, you can replace "LOG" with "LN" if you want to use the natural logarithm function.

Step

Copy this formula to all of the remaining cells in the "B" column for which there are associated "x" values in the "A" column. You should now have a complete table of values. This table will serve as a guideline for Excel to calculate a smooth graph.

Step

Click on the "Insert" tab and from under the "Charts" header choose "Scatter with Only Markers."

Step

Click on the "Layout" tab, click on "Trendline" and select "More Trendline Options."

Step

Select "Logarithmic" and click "Close." This creates a smooth graph that lines up to the table of data you created.

Step

(Optional) Right-click on one of the marker points and choose "Format Data Series...".

Step

(Optional) Click on "Marker Options" and choose "None." This hides the guide points that you used to create the trendline.