In the UK it takes 3.5/4 years. You normally get money from the government while you are researching and then you write it all up into a big book called a thesis. You then have to defend your work to some specialists and if you pass you get a PhD!
Other countries have different timescales, like in the USA it takes 7 years!!
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Marton commented on :
As Miriam mentioned it takes around 3-4 years in most of Europe, and can get quite long in the US