Weight of a large egg
There is indeed a standard for egg sizes. Size M in Europe, corresponding to Large in the US, is roughly 55 grams per egg. This is including the shell, if you have a recipe which doesn't include the shell (e.g. it was developed for pasteurized eggs from a carton), you have to calculate about 5 g of shell for that size of egg. 

You can look up tables of other egg sizes on the Internet, but that's the most common size in supermarkets, and the one most commonly used when developing recipes, so I suppose it is the one you need.