One of the largest stars known is UY Scuti at 1,708 solar radi (diameter of Sol) or 432,450 miles X 1708 = 738,624,600 miles which makes its outer shell fall at the midpoint between the orbits of Jupiter and Saturn.
Playback restricted at the UMG site link.
Youtube link:
https://www.youtube.com/watch?v=zR3Igc3Rhfg&feature=player_embedded
Thanks PIF.