I bet you can Google that question and find a source that will give you a number, say $1,000,000. The fact is your real number will be based on your income at retirement and any other sources of income you will have such as a pension or Social Security.
Whatever your number, remember that is in the future and the younger you are today, the more inflation you must deal with.
For example, say it’s 1991 and the amount you need is $1,000,000 to compliment Social Security in retirement. Now it’s 2021 and that $1,000,000 is the equivalent of $1,960,748.90.