system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the British Pound worth much more than the USD, when it seems like the equivalent goods cost the same face value amount?
gpt
Point of sale costs, government services and methods of taxation all matter.

When you buy X in the UK you're buying all of the labour along the chain.  So if the guy who delivers the package to the store, the store clerk etc. all get paid more in the UK you're paying more money for the same product otherwise.

It's not easy to compare "The US" to "The UK" either.  Costs in New York or London are relevant to averages, but you shouldn't compare the cost in London versus say Texas.

Then you get into other 'costs'.  If you need healthcare in the UK the government has your back.  For that about 10% of GDP covers everyone in the country and provides better care.  In the US if you need healthcare the government might have your back (~7% of GDP) but might not, at which point you pay out of pocket or have private insurance (~10% of GDP).  And lots of stuff like that.  This means the average british person is paying more in taxes towards healthcare, but less money overall for healthcare (and getting better care) compared to the average american.  

Then you have just straight up cultural differences.  Comparing the price of a can of coke between the two places isn't necessarily indicative of 'typical beverage' because the british and americans consume different things.  This applies to cars and houses and expensive stuff too.

So what you do is you start doing complex averaging.  So you add up all the stuff people spend money on, housing, transport, food, healthcare, education (including post secondary), entertainment, power, telecoms etc. and you say what does 30 000 pounds in income get you in the UK versus 51KUSD  in the US?  And currencies float up and down because these are constantly being reassessed and constantly have many factors playing a part, and in the end it's just an average anyway.  Because 51K in New York city is not the same as 51K in Plano Texas, and 30K GBP in London is not the same as 30K GBP in Northern Ireland.  

Oh and how you do taxes is tricky.  The EU is big on value added tax (which is about 22% on average or something), and looks a lot like a sales tax, whereas the US has more income tax.  Some countries are borrowing more than others to provide services etc.  

**TL:DR** there's no simple 1:1 comparison.  It's about the average of all of the spending that happens, which requires considering a LOT of data about a lot of different things.