Now after some more research and the above link this is for permanent wiring.so it isnt ever going to drop wires size down below 14 gauge.
Here is a link Home Depot has for extension cords.
http://www.homedepot.com/c/factors_t...cords_HT_BG_EL
now that we have learned in many ways to find you what an apylance draws we can use the above information to see just how big of a cord we need.
Here is and example.
I have a 50 foot 16 gauge extension cord going to my shed.
all it ever does is turn on two 100 watt light bulbs.
this add up to 1.66 amps the cord is rated for 13 amps.
More that adequate for the use at hand.
In other w0rds no need to drag out the big guns.