A few years back, an author named Lee Eisenberg wrote a personal finance book called "The Number" which was very popular. In the book, Eisenberg talks about the quest to determine one's "number" or the amount of money needed to retire comfortably.
If you have the time to read the book, I do recommend it. But what if you would like to know your "number" and can't commit to reading a book with a couple of hundred pages? I would suggest checking out the "Ballpark E$timate" tool offered by Choose to Save, which is a national public education and outreach program. They offer an exceptionally easy on-line tool that let's you know if you are "on track" for retirement.
To determine your "number" all you really need to know is your current income, your current retirement savings and the number of years until you expect to retire. The tool provides guidance on how much you will likely spend in retirement and it can be tailored to reflect your estimate of your life expectancy.
If you are not the on-line "type" you can also download and print a 2 page worksheet. Either way, the total time commitment is about 10 or 15 minutes and the results are pretty accurate. To access the tool, visit choosetosave.org/ballpark.