It depends. A mechanic friend of mine said anywhere from 70,000 to 90,000 miles. The down side is they cost ~ $9,000 each (total of $18,000) to replace.
In California and New York they are warrantied for 10 years or 100,000 miles. In most of the rest of the country they are only warrantied for 8 years or 80,000 miles. Therefore I conclude that Toyota is very confident that 90% should last 8 years or 80,000 miles.
The 2004 Toyota Prius is 14 ft. 7 in. (175 in.) long.
The 2007 Toyota Prius is 14 ft. 7 in. (175 in.) long.
The 2008 Toyota Prius is 14 ft. 7 in. (175 in.) long.
The 2011 Toyota Prius is 14 ft. 7.6 in. (175.6 in.) long.
The 2006 Toyota Prius is 14 ft. 7 in. (175 in.) long.
The 2014 Toyota Prius is 14 ft. 8.4 in. (176.4 in.) long.
The 2002 Toyota Prius is 14 ft. 1.6 in. (169.6 in.) long.
The 2003 Toyota Prius is 14 ft. 1.6 in. (169.6 in.) long.
The 2009 Toyota Prius is 14 ft. 7 in. (175 in.) long.
The 2001 Toyota Prius is 14 ft. 1.6 in. (169.6 in.) long.
The 2013 Toyota Prius is 14 ft. 8.4 in. (176.4 in.) long.
The 2005 Toyota Prius is 14 ft. 7 in. (175 in.) long.