How Far Is It From Dublin To Melbourne?

I am going to assume you mean Dublin Ireland and Melbourne Australia.  Because those placenames have been borrowed and bestowed upon many other dinky little places world wide, and the combinations are too many too go into here.

Straightline distance along the Earth's surface: about 10,681 miles  17,189 km.  You wouldn't get a direct flight.  Have to change somewhere like Hong Kong or Singapore.  Huge heck of a long way.  20 hours or more in airplanes.

If you measure the straight line flight distance ("as the crow flies"), the total distance from Dublin to Melbourne is 10,692 miles or 17,208 kilometers.