You can find retirement savings calculators at various financial websites, such as money.msn.com, and others, but...
Before, or even after, plugging in rather random numbers on some website's retirement calculator, a better idea is to develop your personal retirement plan using real information.
From there you can develop a reasonable budget that you can test using the best retirement calculator: FireCalc.
Using the budget information derived from your retirement plans, you can determine and evaluate the actual savings amount needed for your specific situation.
Everyone's situation is different, with different goals, spending habits, health needs, and lifestyle plans for their retirement years. (See the page on Detailed Planning Steps, link at bottom of this page.)
You would not want to reach age 60 and realize that you could have retired 5 years earlier with plenty of savings to cover your needs, just as you would not like to be retired for 5 years and find that you won't have enough money for the next 5 years.
Most of the basic retirement calculators you find on the internet are flawed in some way. Either they are unclear about what assumptions they are making, or they don't provide a way to factor in Social Security Benefits, or the assumptions don't match your situation, and so on.
A basic formula for estimating your retirement savings needs involves determining your expenses and budget, calculating the total for the year, multiplied by the number of retirement years you expect. Deduct any income amounts such as Social Security, real estate income, other investment income, and that leaves your retirement savings need.
Your budget should take into account all possible expenses, including replacing cars, appliances, furniture, etc, and vacation/travel plans, hobby expenses, insurance, for example.
One worthwhile test you can apply to your plan is to track your actual spending habits for a month or two and see how close you can come to staying within the budget you developed. With what you learn, adjust your budget, and add categories you may have overlooked.
After that, another test is to use the detailed calculator at firecalc.com to get a probability of success. The FireCalc tool applies various stock market scenarios to your portfolio value to see how often they would support your spending plans.
Here is an example report on an early retirement scenario:
In the example shown, the portfolio has a 97% chance of providing the desired income for the 8 year time period.
FireCalc collects information about Social Security, expected returns, and much more, to provide a very comprehensive analysis of your plans.
See these Detailed Planning Steps you should take as well.