There was a time when the iPhone 6 was still fairly new and a lot of people wanted to know more details about it. They weren’t sure then if they should transfer from using an iPhone 5s to an iPhone 6. When it comes to how thin these phones are, the iPhone 6 is known to be thinner by 0.5mm.
It is also a bit heavier but not so much that you would immediately notice it. Another main difference is the size of the screen. The iPhone 5s will have a 4-inch screen while the iPhone 6 will have a 4.7-inch screen. The difference in the screen is surely noticeable.