How large were Norse dragons?

Question

In chapter 10 of the Saga of the Völsungs, Regin is trying to convince Sigurd that Fafnir is an average size dragon:

"Young am I," says Sigurd, "yet know I the fashion of this worm, and how that none durst go against him, so huge and evil is he."

Regin said, "Nay it is not so, the fashion and the growth of him is even as of other lingworms, and an over great tale men make of it; and even so would thy forefathers have deemed; but thou, though thou be of the kin of the Volsungs, shalt scarce have the heart and mind of those, who are told of as the first in all deeds of fame."

_{Source: The Story of the Volsungs, translated by William Morris and Eirikr Magnusson}

When the pair ride to slay the dragon, however, Sigurd realizes from Fafnir's tracks that the dragon is a tad larger than Regin lead him to believe. Regardless, Sigurd - with a little help from the ever-present Odin - slays Fafnir.

I'm trying to get a basic understanding of the mechanics of dragon slaying in Norse mythology, and the comments on Fafnir's size piqued my interest. How large did the Norse imagine dragons to be? Do any of their legends give explicit information on the size of dragons?

Answer 1

Perhaps fifty foot long

I can actually only think of one other real dragon in "proper" mythology: Nidhögg, which is clearly a cosmological beast and should really not be used as a measure, and if we do, he would have to be taken to be immense: in the final verse of Völuspá he "carries the dead" into the world that has been purified after Ragnarök.

If we look at the sagas, we have a notice in Gull-Þóris saga that he was at the end of his life said to have turned into a dragon and that one was sighted near his home, but there is no notice of the size.

We also have what is not actually a dragon, but a close relative, in the Lindworm that Ragnar Loðbrók fought according to Saxo, which had grown large enough to encircle the bower of Þóra Borgarhjǫrtr.

However, we do have one good source for the size of what is actually called a dragon from the right period, but it is not quite norse: the one that Beowulf fought and lost his life against. It is explicitly said to be fifty foot long (line 3043), so that will have to be the answer.