Unfortunately for our purposes, the Gospels do not provide us with the exact location of the Upper Room. The current site claiming to be the location of the Last Supper was built in the twelfth century. However, it might be close to the original location. Indeed, archaeological excavations on the site have concluded that there was a structure here at the time of Jesus.
The Garden of Gethsemane was located on the Mount of Olives across the Kidron Valley from Jerusalem. The exact location of Gethsemane is also not known. Several sites on the mount have been identified as the exact location of the garden as early as the fourth century.
As the crow flies, these sites are just under a mile apart. Jesus would not likely have walked directly there, however. He would likely have had to walk around the Temple Mount and taken a route across the Kidron Valley that followed the counters of the steep slope. A logical route between the two sites would have followed the bottom of the valley or skirted around the outside walls of the city. Of course, it is uncertain if this was the route used. If so, Jesus and his disciples would have walked about 1.15 to 1.25 miles to get to Gethsemane.