When using the Excel, you may find that the ruler is grayed out and you cannot use it. This is because the "Ruler" by default is gray out in the Normal View and Page Break Preview, and you can use it only in the Page Layout View.
Step 1: Click the View Tab from the ribbon;
Step 2: The Ruler display in different views:
1. The ruler is grayed out in the Normal View;
2: The ruler is grayed out in the Page Break Preview;
3: The ruler is available in the Page Layout View.