How can portfolio diversification be measured? On average, what degree of diversification would you expect to find

Question:

How can diversification be measured? On average, what degree of diversification would you expect to find for a typical equity mutual fund holding large cap stocks?
Portfolio
A portfolio is a grouping of financial assets such as stocks, bonds, commodities, currencies and cash equivalents, as well as their fund counterparts, including mutual, exchange-traded and closed funds. A portfolio can also consist of non-publicly...