Measure distances on your floorplan with the Dimension Line tool, accessible from the Tools menu or the Toolbar above the diagram.
Once a Dimension Line has been created, it can be edited from the Edit Object section in the right-panel. You can also select the tip of the line with your cursor to adjust its length and orientation
Dimension Lines can be "docked" to objects by dropping the end of the line onto one of the available points that appear on the object when hovered over. When this occurs, the base of the dimension line will remain static, while the line itself adjusts its length as the object is moved about the diagram.