I received a used 2 cup Brikka without the measuring cup. Anyone knows what is the volume of this measuring cup?
MT San' answer is not correct. He gives a link for Moka Express measurement. Brikka is different. 2 cup version should be filled with 60-70 ml of water in the bottom chamber.
Check the upper chamber, if you have new version of Brikke (Brikka Elite) there should be a measuremnt mark like on this photo (look for "H20" mark): http://101coffeemachines.info/wp-content/uploads/2018/05/bialetti-brikka-valve.jpg
Actually, this and maybe a bit more has been discussed before in Coffee SE:
Under more details tab of Bialetti's web site, you can find a list of volume's for water chamber, which are: 60 ml for 1 cup and 200 ml for 3 cups. I assume, 2 cup should be 120 ml. The amount of coffee that you should use is also determined by the funnel size under Care Use tab, to use title, 2nd article as :
Insert the funnel and fill it with ground espresso (do not tamp). Remove any coffee grounds on the edge of the funnel
The Bialetti Brikka comes in two varieties. The 2- and 4-cup edition. The water chamber of the 2-cup edition is 100ml and the 4-cup has 200ml volume water chamber.
I'm not entirely certain which measuring cup you are referring to though. Bialetti offers a measuring spoon. However they don't explicitly state the volume of it, so a best guess would be to use a standard "spoon" volume, which is approximately 15ml.
You may be referring to the coffee chamber, which you put, filled with ground coffee of course, into the brewing device. There is also no specification of volume, however the diameter is know and given by Bialetti. The funnel of the 2-cup Brikka is exactly 2 3/8 inches wide (roughly 6cm). Guessing that the height of the funnel (without the spout) should be roughly a bit over half of that (3.5cm maybe judging only by looking at it, so it may be off), the volume of the gasket would be around 100ml as well, calculating the volume of a cylinder. This doesn't account for the fact, that the bottom of the cylinder is slightly convex, but since I don't have a Brikka at hand right now, we are kind of in the guessing game anyways.
However one more thing. To use a Bialetti stove top you don't need any measuring spoon anyways. You just fill the funnel with coffee until it's completely full without tamping. Then you fill the water chamber just right below the safety valve, you screw the top on and you are good to go. The ratios are basically of fixed by design.