You want to protect your tools and property.  You also want to make sure your tools run they way they should, at peak performance.  In order to protect your tools and make sure they run at peak performance, you should understand extension cords and their ratings.  Below is a table of the ratings of extension cords. 

Cord Length (ft.)GaugeMax Amps
251810
251613
251415
50185
501610
501415
75185
751610
751415
100165
1001215
125165
1251215
150165
1501213