Select a curve

When you start the Smart Dimension command, the program prompts you to select an entity.
As soon as you select an entity, the options in the selection list change, depending on the point at which you select the entity: If you select a curve, the selection displays the following options:
Orientation This option is ignored in this case. The orientation is always Distance
Type Enables you to specify the type of the dimension to be created, based on the selection you performed. Select one type from the drop-down list
Properties Displays the Properties dialog box


You can then create a curve length dimension using the option (to be selected in the Type drop-down list):
Curve Length