In ArcMap, each data frame uses a coordinate system to determine map projection. Map units, the units in which the layers in the data frame are displayed and used, are determined by the data frame's coordinate system.
When a projected coordinate system is used in the data frame, the map units are linear units, such as feet or meters, and when a geographic coordinate system is used, the units are in degrees.
To change the distance measurement to linear units, follow the below steps:
1. Open the Data Frame Properties dialog box; click View > Data Frame Properties.
2. On the Coordinate System tab, set the data frame’s coordinate system to a projected coordinate system.
Changing the coordinate system of a data frame doesn't alter the coordinate systems of the source data in the data frame.
3. On the General tab, under Units, change the default display to linear units.