Forget about inflation and forget about cost of living increases for the moment. Just think about what your life costs you at the moment and what it would cost you if you were retired instead of working. Some expenses that you can reasonably expect to be lower if you choose to lower them are housing, car expenses, savings, and even taxes if your income needs drop you into a lower tax bracket or if a significant portion of your retirement income is supplied by a Roth IRA . Unless you are crippled you will want to do something with that time. Travel, golf, movies, plays, eat out, etc.
Every activity seems to cost money.
Also most of us have experienced a continual higher standard of living as we have aged. Our 30s were higher than our 20s, our 40s were higher than our 30s, etc. This expectation of ever increasing standard of living does not go away. Again, there's good news coming on that front. In the meantime, I hope this kind of generalized discussion has stimulated you to develop a ballpark figure in your mind of the kind of income, in today's dollars, that you would allow you to maintain your current lifestyle, with appropriate modifications, in retirement.