Sketcher > Dimensioning Sketcher Geometry > Working with Dimension Tools > Normal Dimensions > To Create an Angle Dimension for an Arc
  
To Create an Angle Dimension for an Arc
1. Right-click in the Sketcher window and choose Dimension from the shortcut menu or click Sketch > Normal.
2. Click one endpoint of the arc.
3. Click the other endpoint of the arc.
4. Click the arc.
5. Click the middle mouse button to place the dimension. An arc length dimension is created.
6. Select the dimension. Right-click and choose Convert to Angle. The dimension is converted.