How long is a generation?

The older definition of a "generation" (the average interval between the birth of an individual and the birth of its offspring) was 20 or 25 years.

However, genealogical studies have revealed that this is too simplistic and can result in large inaccuracies during statistical calculation.

According to Ancestry.com, a calculation based upon "three generations per century (33 years each) for male lines and 3.5 generations per century (29 years each) for female lines" leads to much more accurate estimates.