how much; how many; to what extent
Used to ask about quantity, degree, or extent. Can also be used in exclamatory or rhetorical expressions.
How long do I have to wait?
No matter how much I practice, I can't get better.
I don't know how many people will come.
どれほど is more formal and literary than どれだけ, and tends to appear in written or formal speech rather than casual conversation.
どれだけ and どんなに can both mean 'to what extent', but どれだけ often has a quantitative nuance (how much/how many) while どんなに emphasizes emotional degree.
Compound of どれ (interrogative pronoun) + だけ (extent/amount). The kanji spelling 何れ丈 is ateji and rarely used.