According to the university, Betelgeuse's radius is about five astronomical units
This shows how gigantically HUGE this thing is. For those who don't know, an AU (astronomical unit) is the average distance from the Earth to the sun. Call it 143,598,000 kilometers. The
radius of Betelguese is five of those. 717,990,000 kilometers. That's the radius. The diatmeter would be twice that. Betelguese is 1,435,980,000 kilometers in diatmeter.
EDIT: Sorry, the wiki on astronomical units actually mentions Betelgeuse as having a
diameter of 5.5 AU. Rougly 789,789,000 km.
The mean diameter of Betelgeuse is 5.5 AU (511,258,000 mi.).
I'll leave both up because I don't know which one is the actual size.