How to Calculate a Standard Error of the Mean in Excel
This guide assumes you have already taken the average or mean.

 

1.      Place the cursor in the cell where you wish the standard error of the mean to appear, and click on the fx symbol in the toolbar at the top.

2.      A menu will appear that says “Paste Function”.  Select “Stastical” from the left hand side of the menu, if necessary.  Scroll down on the right hand side of the menu and select “STDEV”; then click “OK”.

3.      Click on the picture of the spreadsheet, and highlight the numbers you averaged earlier, just as you did when taking the average.  Hit enter, and “OK” to calculate the standard deviation.

4.      With the cursor still on the same cell, now click in the formula bar at the top of the spreadsheet (the white box next to the “=” sign) to put the cursor in that bar so you can edit the formula.

5.      Put a “(“ in front of STDEV and a “)” at the end of the formula.  Add a “/” sign to indicated you are dividing this standard deviation.  Put 2 sets of parentheses “(())” after the division symbol.  Put the cursor in the middle of the inner set of parentheses.

6.      Now click on the fx symbol again.  Choose “Statistical” on the left hand menu, and then “COUNT” on the right hand menu.

7.      Click on the spreadsheet picture in the pop-up box, and then highlight the list of numbers you averaged.  Hit enter and “OK” as before.

8.      Move the cursor to be between the 2 sets of parentheses, and type “SQRT”.  Hit enter.  The standard error of the mean should now show in the cell.  Your formula in the formula bar should look something like this, “=(STDEV(A1:A2))/(SQRT(COUNT(A1:A2)))”.
(This formula would calculate the standard error of the mean for numbers in cells A1 to A2.)

NOTE:  We have calculated standard error of the mean by dividing the standard deviation of the mean by the square root of n.  Given the formula that Excel uses for calculation of standard deviation of the mean, this gives the standard error of the mean after adjusting for a small sample size.  This is usually the case in physiology experiments.  The formula would be different with a very large sample size.  I do not know why Excel still does not include a formula for calculating the standard error of the mean.