What is the size of the sun compared to the size of a supernova?

Where the solar wind ends and the interstellar gasses begin is considered the edge of the solar system (and arguably the edge of the sun - yes that DOES mean all of the planets {even Pluto} are inside the sun).  Its roughly 8 billion miles from the sun and of course no supernova is that big.  Of course it is not a globular shape, either...  Anyway, the solar wind is made up of molecules heated to supersonic speed in the sun and released into space; the sun's atmosphere, if you will.  You could argue that the "ultimate" size of a super nova is the size the gases released from the explosion reach before they are "stopped" by the interstellar wind.  Problem is, they aren't really stopped, its more like two rivers joining, they mingle with the interstellar medium, but are still detectable for millions of years after the explosion.  there are some beautiful pictures of nebula (I think the crab nebula is one (?)) formed from supernova explosions online.  A nebula is just the ionized gases from the explosion.  (this kind of nebula is, anyway).  Anyway, the largest supernova is just a bright speck of light while some nova are huge, on a galactic scale (hundreds or thousands of light-years across).  (But still tiny on the scale of the superclusters or of the universe over all).

"Size" of a supernova is not a well posed question.

If you are talking about spatial extent, a supernova remnants can be quite large (parsecs across) and expand over time, so there is no constant size.   The crab nebula (see image below)  is still a somewhat young remant a 1000ish years old and is 12 lightyears across.  For comparison if the sun was the size of an orange,  the crab nebula would be roughly the size of the Earth.

You could compare the light energy output of a supernova to that of the sun.  A SN releases approximately the same energy in photons(*) in one second as the sun will over its 10 billion year lifetime.

(*) Most SN energy (99%) is carried away from the parent star in a rush of highly relativisitic neutrinos and go essentially undetected.