Dragnix.Net

What size does the wings of a dragon have to be for it to fly?

That really depends on the overall weight of the creature. I'll have to dig through numbers of different flying things to make a guess. But I would say a large wing is needed. They may be soaring creatures rather than flapping creatures. So they would need a large amount of surface area on the wings to add more lift.

Wikipedia is your friend here:

http://en.wikipedia.org/wiki/Quetzalcoatlus
http://en.wikipedia.org/wiki/Pterosaur_size

This should tell you about the upper limits of animal flight.