There are three different methods for measuring distances and objects in your circuit. You may add dimensions to your circuit, use the bounding box information in the status bar at the bottom of the project editor window or open the Measuring Tool.
You may add dimensions to display the distance between any two vertices in your circuit. This allows you to determine the distance quickly and leaving multiple dimensions displayed on your circuit may often aid in making the drawing clearer. See below for a link to how to add a dimension.
When a polygon or set of points are selected, the dimensions of the bounding box of the selected object(s) appears in the cursor section of the status bar. You may use this to determine the size of an object or the distance between two points in your circuit. In the case of the two points, the bounding box provides the distance in the x and y plane.
It is also possible to measure distances in your circuit by using the Measuring Tool provided in the View menu of the project editor. For details on using the Measuring Tool, see Edit - Measure.