Sketcher > Dimensioning Sketcher Geometry > Working with Dimension Tools > Normal Dimensions > To Toggle Between Diameter, Radial, and Linear Dimensions
  
To Toggle Between Diameter, Radial, and Linear Dimensions
1. Select a dimension to toggle.
2. Right-click and choose one of the following from the shortcut menu:
Convert to Diameter
Convert to Radius
Convert to Linear
The dimension is converted.