Analyze a design > Measure > To measure the diameter of a circular object
  
To measure the diameter of a circular object
Measure the diameter of a circular object as follows:
1. Click Analysis and then, in the Measure group, click the arrow next to Rad/Dia.
2. Click Diameter. The Measure Output and Distance dialog boxes open.
3. Click the circular object (for example, arc, circle, cylinder).
4. The application displays the length of the object in the Distance Output field.
5. Click the green arrow button to send the measurement to a command.
6. Click the green arrow and calculator button to send the measurement to the calculator.