Arc Dimensions
The default dimension type for an arc is radius. You only need to select
the arc for this dimension type.
You can dimension the true length of the arc.
To dimension the true length of an arc:
In an open sketch, click Smart
Dimension (Dimensions/Relations toolbar) or Tools, Dimensions,
Smart.
Click the arc.
Click the two endpoints of the arc.
Move the pointer to show the dimension preview.
Set the
value in the Modify box and click
.
Click to place the dimension.