The structure of post-grad programs is fundamentally different between the two. In the UK you generally have a Master's already before beginning a PhD, while in the US you typically enter a doctoral program directly from undergrad and pick up a Master's "on the way".
6 years is probably pretty typical in the US for the sciences. For the humanities it's generally even longer (often due to the need to work to support oneself due to lack of funding). I recall seeing somewhere that the _median_ history PhD takes 11 years.
Edit: seems I misunderstood the UK structure, perhaps I was confusing with continental Europe? Not sure about the time difference in that case.
> In the UK you generally have a Master's already before beginning a PhD
No that's the opposite - in the UK you normally either do a masters or a PhD but not both. You can leave your PhD partway through and you get a masters though, maybe that's what you mean.
A canonical PhD in the UK is three years of undergraduate and three years of PhD, so six years from leaving high-school equivalent. Some people take one or two extra years in practice.
I had a colleague in Austria who did a full high-quality PhD with top-tier publications in just two years!
"In the UK you generally have a Master's already before beginning a PhD"
That's not my experience - you can generally go straight from an undergraduate degree to doing a PhD - I did and most of the people I knew did the same (and the people who had Masters either had done MEng as a first degree or had MSc conversion courses).
NB There is also the weird thing where some UK institutions give you a MA for still existing after a few years....
6 years is probably pretty typical in the US for the sciences. For the humanities it's generally even longer (often due to the need to work to support oneself due to lack of funding). I recall seeing somewhere that the _median_ history PhD takes 11 years.
Edit: seems I misunderstood the UK structure, perhaps I was confusing with continental Europe? Not sure about the time difference in that case.