There is no definite boundary to the solar system.
The center of the system is the Sun.
The farthest identifiable bit of the solar system may be an icy cloud formation called the Oort Cloud from which comets appear.
It extends about 2 light-years away.
The nearest star to the Sun is Alpha Centauri, 4 light-years away, which may have its own solar system.
By combining this information and splitting the distance between the two stars, we come up with a probable answer.
The solar system is about 2 light-years in radius.