Median household incomes $84k Cali vs $42k UK.

They're post-tax and don't factor major expenses like healthcare, household bills in general are almost double in California, but yeah, the average Californian is probably wealthier.

People in CA would go to In-n-Out anyway. https://www.fastfoodmenuprices.com/in-n-out-prices/ at (2.463+2.163+1.872)1.0725 = $18.88.

Even if you double the fries because they're not "large" you're still under $25. Five Guys is batshit insane.

In-n-Out burgers are smaller though, so I usually get two whereas I'll only have one at Five Guys.

Still, Five Guys is a bit over the top expensive so I rarely go there.

True, and the "default" burger at In-n-Out is a double/double but even that's still less calories than Five Guys.

But Five Guys is up at or above Smashburger pricing, so I'm not sure what they're doing.

Five Guys and In N Out are competing in different market niches. In N Out is operating in the fast food bracket, competing with McDonalds and Jack In The Box (both of which it's cheaper than, remarkably). Five Guys is trying to be a more premium burger place, in the fast-casual market. In that niche, we can compare it to Panera or Blaze Pizza or the like, where a $15-20/person bill isn't unusual at all.

I understand the market they're obviously aiming at, but it feels like a cheap In-n-Out replacement around here. For those prices I'd go to a roadhouse or Smashburger or the local bars or similar.

They do have that weird soda robot, so there's that.

Costs vary quite a lot by location in California so averaging over the state is losing some information.

At my local Five Guys in LA, a cheeseburger is $11.79, compared to $9.84 on that site. Ten times out of ten I'd just go to In-N-Out.