You can define a letter grade scale so that each numeric course grade will be converted automatically to a letter grade. Follow this procedure.
From the course page, click on the link on the left side under Administration.
From the pull-down menu, under Letters, select .
Click the checkbox.
You will see a sequence of pairs of fields, one for the letter and one for the lower boundary of that letter. Initially you will see grades A, A-, B+, B, B-, C+, C, C-, D+, D, and F, but of course you may use any set you like.

To change the lower bound for a grade, use the pull-down menu labeled Letter grade boundary and select the new value. Grades exactly equal to the boundary will fall into the higher category. For example, if 77% is the lower bound for C+, an average of 77% will be called C+, not C.
If you don't want to use a particular grade, set the pull-down menu for that grade to .
When you have everything set up, click .
Next you will need to add a letter-grade column to the gradebook. From the pull-down menu, under Categories and items, select .
To add a letter grade for the entire course, click the
icon in the Actions column for the course.
You are now in the Edit category page. In the Category total section, click the button.
In the pull-down menu, select one of the choices that starts with Letter.
The choice shows only a letter grade for the course.
The choice shows both a letter grade and a percentage based on 100%.
The shows the numerical average, in case you are using a basis other than 100%.
Click .
You may use a similar procedure to attach a letter grade to any other column.
If the changes you have made don't show up immediately, go into the Grader report (from the course page, → → ), click on , click on , and then click on .