Hi! John's comments apply to MBD/3DA workflows. If you want to display sketch dimensions in fraction in a part or an assembly, here is what you need to do.
1) Go to Tools -> Document Settings -> Unit -> Model Dimension Display = Precise Value.
2) Go to Parameters table -> click on the small right-pointing arrow button in the parameter input field -> select "Fractional"
This will help you show any decimal value in fractional. When you enter a sketch dimension value, you can also type in fraction like 4'3/8" and it should be displayed as such.
Many thanks!
Johnson Shiue (johnson.shiue@autodesk.com)
Software Test Engineer