If you go to a good knitting shop, bring your pattern and ask for help if you want to use a yarn that is different from the original. There will surely be ladies to assist the calculations.
And ask if you can take some yarn and bring back if unused. My favorit shop does that so you can get back up, just in case.
If you go back later to get more, it may be a slight variation in color (check the nubers on the tags!!!) or be sold out.
European balls of yarn are most often packed as 50 g. (I am German). Some big coils come in multiples of that. Very few only (baby sock wool, e.g.) come in 25 g.
And then European coils measure in meters, not yards. But that you can calucalte, too. Pretty much add 10 % of the yards and you are there.