One of the questions I am frequently asked is "What length cable do I need?".
The answer is mostly up to personal preference. If you don't mind a lot of stitches bunched together then a very short cable will work just fine.
If the project has any corners (like a center out triangle shawl), then a longer cable will be more comfortable. My most commonly used cables are 1" and 8". In the photos is a 6" (15cm) hook with 1" (2.5cm) cable with a 150 stitch row.