How to check coolant/water ratio

[asifg]

Hi All

I've got a B7 RS4 and I understand that the water/coolant ratio should be 60/40.

Can you advise the best way of checking? My tank is a little low so I want to ensure that I top it up correctly.

I've seen some devices on Amazon, but would rather get one that people use already and works with the type of coolant we have, as apparently not all do (according to some reviews on Amazon).

Cheers