OK, I said i3 as Intel try and hide their die sizes these days and I was too lazy to dig around and do maths.
i5 8250u is 122mm^2 on a 14nm process:
https://en.wikichip.org/wiki/intel/core_i5/i5-8250uAssuming Intel are right that their process is better so their 14nm is equivalent to someone else's 10nm, then that means that is close enough comparable with the A11 on feature size. So the A11 is 72% of the size of an i5.
I'm far from an Apple fanboy, I don't own *any* of their kit, just running the numbers those are pretty big for a phone.
I tried to find the die size for a raspberry pi, but got bored :D Note the cost of getting masks done at these feature sizes it well out of hand, I really don't see that it makes sense on a small chip to bother when you could just make a bigger 28nm chip for peanuts and get it made pretty much anywhere. You have to really care about having a lot of kick in a small space.