The manufacturer recommends 22" for the driver side and 19" for the passenger side. I've always been bothered by the amount of area on the high part of the driver side that the wiper doesn't reach so I have always installed 24 and 17 instead with much better results.
I do not see a rear wiper blade listed for a 2008 Ford Focus. If there is one on there, it must be a special Ford-only wiper (which is rare for Ford - they normally go with universal wipers). I do see that 2000-2007 Ford Focus has a rear wiper listed for both the hatchback and wagon. So, possibly you have the year wrong? If so, the wiper blade videos for hook-end wiper arms will show you how to change the rear (as well as front) wiper blades.
The 2003 Ford Focus has the most common hook-end wiper arms. See the Sources and Related Links section below for installation videos. Also, purchase the replacement blades first and there will be additional instructions/illustrations on the replacement packages. Locate and press the tab or button where the wiper blade is inserted into the hook of the wiper arm and pull wiper blade out of hook. You may have to rotate and flex the blade to make enough clearance for the hook to pass through.
The 2007 Ford Focus has hook-end wiper blade arms. There's a little tab or button where the wiper blade is inserted into the hook. Press tab and pull wiper blade out of hook. Sometimes you have to rotate and flex the blade a little bit to allow enough clearance. See video below.
On the 2003 Ford Explorer the wiper blade sizes vary depending on the trim-level of the Explorer. See sources and related links below to lookup wiper blade sizes for exact make, model, year and trim.
The 2001 Ford Focus takes 22" drivers side and 19" passenger side replacement windshield wiper blades. (If applicable, the rear wiper blade on the hatchback is 14" and the rear wiper blade on the wagon is a 10" or 11"). See sources and related links below for more information.
The hardest part is finding the replacement blade. See sources and related links below. After having new wiper blade in-hand, press the button or tab where the wiper blade is inserted into the hook on the arm and pull wiper blade out of hook. You may have to rotate and flex the blade to make clearance for the hook.
The 2004 Ford Focus takes a 22" drivers side wiper blade, a 19" passenger side wiper blade and the hatchback takes a 15" rear wiper blade (14" will work too) and the wagon takes a 10" rear wiper. See sources and related links below for more information. Since there are over 22 different wiper arm attachments, do not buy wipers just by length only - be sure to lookup exact wiper blade part numbers by vehicle make, model and year for the brand wiper you decide to purchase. This ensures correct length AND correct attachment.
11 inches: just installed one myself yesterday.
How do you change the wiper control module on a 2006 Ford Focus
It may vary by vehicle year and country the vehicle was produced in, however most Ford Focus' have the most common hook-end wiper arms. See sources and related links below for installation videos. Also, purchase the replacement blades first and there will be additional instructions/illustrations on the replacement packages. Locate and press the tab or button where the wiper blade is inserted into the hook of the wiper arm and pull wiper blade out of hook. You may have to rotate and flex the blade to make enough clearance for the hook to pass through.
The 2008-2010 Ford Focus has the most common hook-end wiper arms. See sources and related links below for installation videos. Also, purchase the replacement blades first and there will be additional instructions/illustrations on the replacement packages. Locate and press the tab or button where the wiper blade is inserted into the hook of the wiper arm and pull wiper blade out of hook. You may have to rotate and flex the blade to make enough clearance for the hook to pass through.
The 2003 Ford Taurus has the most common hook-end wiper arms. See sources and related links below for installation videos. Also, purchase the replacement blades first and there will be additional instructions/illustrations on the replacement packages. Locate and press the tab or button where the wiper blade is inserted into the hook of the wiper arm and pull wiper blade out of hook. You may have to rotate and flex the blade to make enough clearance for the hook to pass through.