Note: This post is 7 years old. Some information may no longer be correct or even relevant. Please, keep this in mind while reading.
The apparent diameter of Jupiter varies with the Earth-Jupiter distance. Depending on the distance, the apparent angular diameter of Jupiter is between approx. 0.5 and 0.8 arcminutes. For best astrophotography results, one should pick a time when Jupiter is closest. Similar to my plot of the apparent size of Venus, I wrote a short program to plot Jupiter’s apparent diameter for the time period 2017-2026 (see featured image).