I’ve seen suggestions to save 15 to 20 times whatever income you’ll in retirement. So if you think you’ll need $30,000 per year, you’ll need to save $450,000 to $600,000 by retirement. But that’s just a base calculation to get you started…

And remember, Financial independence is where the interest your money earns is greater than your expenses, no matter where/when that may be.
If your expenses are $30,000/year, and you can get 8% on your savings, then you’d need $375,000 invested. If you can get by on $20,000, then you’d only need $250,000 at that same 8% in order to be Financially Independent. If you are able to save that amount by age 50, then you’d be FI, and you can choose to work, or retire – your choice.