The exact location of the house in which the Upper Room where Jesus had His last meal with His disciples is uncertain. However, it was probably located somewhere within the area known as the "Upper City," which is in the southwestern part of Jerusalem.
Gethsemane was an olive grove located outside of the Susa Gate, the eastern gate into Jerusalem.
Judging by the scale on the map listed below, the distance between the Upper Room as indicated on that map and the Garden of Gethsemane would have been approximately one mile if it had been possible to travel directly from one place to the other. If Jesus and the disciples went around the Temple area instead of passing through those grounds, the distance would have been somewhat longer.