Choose Inspect tab→2D Measure group→Total Length 
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Click on the element or elements that you want to add to the select set.
The sum of the lengths of the selected elements is displayed in the Length box on the Measure Total Length command bar.
To begin another total length measurement, click Deselect on the command bar, and then select the elements.
Tip:
In Draft, when measuring within or to a drawing view, you can choose to display the value using the model distance or a user-defined distance by selecting a scale option on the Measure Total Length command bar.