Demographics of Wizarding Britain

"Let's say three thousand [in Britain]... but don't hold me to these figures, because that's not how I think."
- JK Rowling

Appoximate Pop of Britain = 62 000 000 people

= 1 wizard or witch for every 20, 666 (recursive) people. Assuming this distribution is average for every region (highly unlikely) these are the estimates for magical populations around the world.

I made this thread to clear up confusion, as I had a reply to my article about something related to it. I gathered a lot of information before writing this.

Since this thread addresses a rather small issue, I could expand it to include many other topics about Wizarding Britain?

Anyway:

Overall population of Wizarding Britain:

The population of Wizarding Britain (and Ireland) seems to be around 12,000. We come to this figure by the few instances that Rowling points out about population in the Wizarding World.

1. Harry estimated that 200 Slytherin supporters arrived at a quidditch match. This means that there are around 800 students in total at Hogwarts.

This is a strange number, considering there were only about 40 students in Harry's year. (~10 per house) However, Harry's year could have an especially low number, due to a very low birthrate during the First Wizarding War.

2. By the demographics of muggle Britain, children aged 11-18 make about 10% of the population. Since wizards and witches live for much longer, the percentage of students would be even lower. If we take it at 6%, the total population becomes 12,000.

This makes sense. Harry observes hundreds of wizards in the Ministry atrium, and also is told that 500 ministry workers built the quidditch stadium.

3. Great Britain has about 1% of the world population. Assuming that it also has 1% of wizarding population, the population of the Wizarding World is around one million.

Again, this makes sense. The Quidditch World Cup stadium could hold 100,000.

Purebloods
A pureblood is a wizard or witch who have a purely of approximately pure magical heritage. This means there are no muggles in their close family trees, though this very rarely is ever the case. Another description is that a wizard or witch is pureblood if all four of his or her grandparents were wizards and witches.

If we take the former description, only a few families are still extant, and due to inbreeding, the number of true purebloods is always either stagnant decreasing. Currently true purebloods represent about 3% of the population.

If we take the latter description, purebloods are not all that uncommon. By general count of Harry's year-mates, about 25% of Wizarding Britain is pureblood.

Half-Blood
A half-blood is either a wizard or a witch with known magical heritage, or a wizard or a witch who's grandparents were both magical and non-magical.

Either way, half-bloods number far more than either muggleborns or purebloods. This number would go from 70% to 95%, depending on the definition.

Since Magical genes are dominant, squibs are very, very rare.

Muggleborns
Muggleborns are wizards or witches who have no magical heritage whatsoever. They are quite rare. Apparently, Harry's year had just two (Hermione and Justin.) If we take this number and apply it to the Wizarding Britain in general, about 2% of Wizarding Britain is muggleborn.

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Summary:

Population of the Wizarding World: Over a million
Population of Wizarding Britain (and Ireland): ~12,000
Pure-bloods in Britain: 300-3,000 (3%-25%)
Half-bloods in Britain: 8,500-11,500 (70%-95%)
Muggleborns in Britain: 350 (3%)
Squibs in Britain: ~100
Overall Ratio of Wizards to Muggles: 1 : 5600 (Or <0.02%)

Demographics from a Biological Standpoint

What JKR has told us:
Muggleborns come from parents with the potential for magic somewhere in their genetic code.
Squibs are born from "pureblood" families
Most pureblood familes are not completely pure.
The Magical Gene is dominant.

Most likely scenario:
The ability for magic is not carried on one gene. It is shared between genes.
This is known as a dihybrid cross (when two genes are involoved - there could be more).

Outcome:

Halfbloods: 56.25%
Muggleborns: 18.75%
Purebloods: 18.75%
Squibs: 6.25%


Also, we have this from ages ago.

HPL and HP wiki had this ages ago, but it was mostly guesswork. JKR hasn't ever given the number of wizards, at least I dont think so. Various sources say 3000 wizards and witches but I think that is too little

Your right about Squibs, I read that somewhere but I guess I read it wrong.

How do you get the outcome ratio's? Even in canon, muggleborns are quite rare.

It's just genetics. In a dihybrid cross, the outcome ratio is always 9:3:3:1, so you take each number and divide by 16 to get the percentage.

Also, if you include squibs as part of the pureblood population (which Shylock was doing in the letter) 18.75 + 6.25 = 25%

With the canon rarity, I always assume what I see in the books isn't all there is. It's just what's relevant to the story.

I did for a while subscribe to the idea that "bloodedness" was just a social construct used to repress people, but then I realised that squibs prove it has a genetic determinant. See, squibs are shameful to their families, they get sent away to live as muggles but they still have part of the magical code in their genetics. So they breed with muggles and then suddenly, a muggleborn pops up and nobody knows why they're magic. It's because they're the descendant of a squib eventually making the right genetic combination again.

I actually used purebloodedness to teach myself biology.

Merged with the Magical Populations estimate from last year.

Did you take population growth into account, Frank? Remember PA takes place in 2026.

Nope, the figures are for pre 2000. However, I don't think that there would have been any growth, considering the war and the plague in recent years. It could be that the population has decreased from 12,000.