i mean, i've never needed to divide the size of a standard sheet of paper - if i need a smaller variant, i can just fold it in half and cut it. when working with paper, it's pretty easy to do physical math, and you rarerly need something that's perfect down to the millimetre
regarding the size- it's just something you learn through life. school supplies lists typically specify the size of notebooks and paper you need to buy in centimetres, so year over year, you quickly learn that A4 is 22:29.7, and the slightly bigger standard notebooks are 24:32
i just assumed people used 3rd party services for ease of use or faster transactions, seems so wild that you'd not be able to send money using your bank to me
here it takes 1-2 business day for a free wire transfer from one bank account to another, and you can do it in your banking app or on the bank's website. you just need to authenticate with your online pin code. you can also pay 1€ to get a <24h transfer
it's honestly much better than using a third party service, since pretty much everyone has a bank account, and pays using a card tied to that account directly