harry potter - What percentage of wizards are born from wizard families?

I was looking at a comment here, and realized that I don't know what percentage of wizards are born to wizard families, and what are born to muggle families? Anyone out there know the answer?

Answer

In Chamber of Secrets, Ron says,

“Most wizards these days are half-blood anyway. If we hadn’t married Muggles we'd've died out.” (CoS – Chapter 7)

Sirius Black tells Harry in Order of the Phoenix that most “pure-blood” wizarding families have both Muggleborns (Ted Tonks) and half-bloods (Nymphadora Tonks) in their family tree, but don't want to acknowledge it. He also notes that there are so few "pureblood" families left that they are, by that point, all interrelated.

“The pure-blood families are all interrelated. If you’re only going to let your sons and daughters marry pure-bloods your choice is very limited; there are hardly any of us left.” (Sirius Black – OotP – Chapter 6)

On her website, J.K. Rowling says:

Don’t forget that, as Sirius revealed in Order of the Phoenix, none of these families is really ‘pure’ – in other words, they merely cross Muggles and Squibs off the family tree and pretend that they didn't exist. But yes, the number of families claiming to be pure is diminishing. By refusing to marry Muggles or Muggle-borns, they are finding it increasingly difficult to perpetuate themselves. This subject is touched upon in Half-Blood Prince.

She also says:

The expressions ‘pure-blood’, ‘half-blood’ and ‘Muggle-born’ have been coined by people to whom these distinctions matter, and express their originators' prejudices. As far as somebody like Lucius Malfoy is concerned, for instance, a Muggle-born is as ‘bad’ as a Muggle. Therefore Harry would be considered only ‘half’ wizard, because of his mother’s grandparents.

If you think this is far-fetched, look at some of the real charts the Nazis used to show what constituted ‘Aryan’ or ‘Jewish’ blood. I saw one in the Holocaust Museum in Washington when I had already devised the ‘pure-blood’, ‘half-blood’ and ‘Muggle-born’ definitions, and was chilled to see that the Nazis used precisely the same warped logic as the Death Eaters. A single Jewish grandparent 'polluted’ the blood, according to their propaganda.

It appears that “pure-blood” families are becoming less prevalent; half-bloods comprise the majority of the Wizarding population; Muggleborns are less prevalent than half-bloods, but are perhaps a slightly higher population than pure-bloods. If I were to throw out some numbers, I might guess 15% pure-blood, 65% half-blood, and 20% Muggleborn. Something along those lines.

It’s interesting that Muggleborns are descended from Squibs, who are pure-blood wizards who lack the dominant magic gene (but who apparently still carry it as a recessive trait).