I watch, listen to, and read about finance content regularly. I'm certainly no expert, but I've seen estimates online anywhere from $500,000 to $3 million and up.
As Templar said, it's all highly individual. Someone in CA is generally going to need a lot more money than someone in Kansas (which came up in a Google search of one of the states with the lowest cost of living.)
And there are so many other factors that have to be considered: married vs. single; dependents or not (many older Americans are now raising/paying for grandchildren); health conditions (someone with chronic health problems will need more than someone with better health); and so on.
I've have also heard that health coverage can be the deal-breaker -- some people have enough money to retire and cover their living expenses, but only if they can get on some kind of health plan. If they're not old enough for Medicare (and apparently there are a lot of things it doesn't cover, requiring some to take on the cost of additional supplemental plans,) many continue to work if their job offers health insurance.
There are lots of retirement estimation tools available online. Just Google things like "Retirement Estimate Calculator," as well as videos on YouTube. Some are free, but some charge a fee. YouTube can be a good guide as to which calculator might be best for you, and how to use it.
But of course, none of these tools can claim total accuracy and must be taken with a large block of salt, as nothing can predict the curveballs we all face in life.
Hope this helps and best wishes to you!