How much bigger is the sun than Mercury?

Depends on whether you are comparing diameters or volumes.

has a diameter of: ##1,392,000km## Mercury has a volume of: ##4,879 km## The sun is ##(1,392,000)/(4,879) = 285## times bigger

The sun has a volume of: ##1.41×10^(18)km^3## Mercury has a volume of: ##6.083×10^(10)km^3## The sun is ##(1.41×10^(18)km^3)/(6.083×10^(10)km^3) = 23,179,352## times bigger