Is a Social Security benefit calculated in the same way as a FERS or CSRS benefit?

No. The Social Security benefit involves a longer working period and adjustments of actual earnings over that time, with a multi-layered formula designed to favor lower-income earners.

Social Security mails annual benefits estimates to workers age 60 and older as well as every five years starting at age 25, to those who are not already receiving benefits and who have not created an online account at www.socialsecurity.gov/myaccount. Those with such accounts may request an estimate at any time. In some cases statements may be available upon request through local Social Security offices.

That site also has calculator functions to estimate your benefits under different scenarios.