Butter size of an egg equals how much butter?

To help you, I need a bit more information. Do you mean:

* "How much butter is in an egg?" - This is a bit of a trick question, as eggs don't contain butter.

* "How much butter is roughly the same size as an egg?" - This would depend on the size of the egg.

* "How much butter is in a recipe that calls for 'the size of an egg' of butter?" - This is a confusing way to measure butter, and it's likely a typo.

Please clarify your question so I can give you an accurate answer.