Figuring out what size to buy takes only a couple of clicks.

For the most accurate determination, do it two different ways (A and B below) and pick the larger size.

A. First, use this chart and jot down the size you get.

B. If you're in front of your computer and it's got at least several years of your files (i.e., it's not a new PC with very few files), take an extra minute or so with these steps, which start by determining the total size of your files:

1. Click on the Start button and then right click on Documents or My Documents and look at Properties to make a note of the current size. If you have Windows^® XP or 2000, jump to step 4 because My Documents contains Pictures, Music and Videos.
   
   
2. For Windows^®Vista^® repeat step 1 on Pictures, Music and Videos, getting the size of these three additional folders; if you don't see Videos, enter Videos in the Search box that opens above the Start button.
   
   
3. Add those four gigabyte (GB) sizes; if any of the sizes are in megabytes (MB), divide them first by 1000 to get everything in GBs before you add them.
   
   
4. Pick a Back in a Flash^® size at least 50% greater to allow for the files you will create or alter over the next several years.

C. If you did A and B, use the the larger of the two.

As an example with Windows^®Vista^®, Documents might be 158 MB (5,000 2-page letters), Pictures 1.11 GB (700 pictures from a 4 Megapixel camera plus others from a cell phone or downloaded from the Web), Music 893 MB (230 songs), and Videos 162 MB (75 minutes of YouTube-type videos), for a total of 2.32 GB. Add 50% for growth and you get 3.48 GB. The smallest Back in a Flash^® with 3.5 GB would be suitable and last several years; the 7.5 GB size would last longer before filling up.