How far away is Jupiter from Saturn?

Jupiter has orbits at a distance of from the sun of ~ 5.2 AU. It has a orbital period of 11.9 years, it takes just shy of 12 years of Jupiter to go around the sun. Saturn orbits at a distance of 9.5 AU with a period of 29.5 years. In the pictures, the Sun is in the middle as a dark orange circle, Jupiter is a orange-yellow circle with a red spot closer to the Sun, and Saturn in the orange-yellow circle with a ring further from the Sun.

Since they are both constantly in motion, and they are NOT going around in the same time their distance to each other is constantly changing. The closest they get is at "opposition" where the sun, Jupiter and Saturn all line up. Shown in the picture. There distance here is the difference between their orbital radii.

#d = r_{Saturn} - r_{Jup iter}#
#d = 9.5# AU #- 5.2# AU
#d = 4.3# AU

Notice that they are both going in the same direction.
There are going to line up the other way at "conjunction," this time with the sun in the middle, this is the furthest they can be from each other. The distance is the sum of their orbital radii.

#d = r_{Saturn} + r_{Jup iter}#
#d = 9.5# AU #+5.2# AU
#d = 14.7# AU

Notice that conjunction occurs BEFORE Jupiter has made it completely around the sun and Jupiter has traveled though a bigger angle then Saturn. This is because of the difference between their periods, it takes Saturn much more time to complete a revolution.