What gauge cord (10,12,14,16) to plug in block heater?
 

I'm told the block heater on my '03 2500 5.9L draws a lot of amps. What gauge extension cord should be used for this? Any advise is appreciated! Thank you.

Block heater are normally 750 watt's Divided by 120 volts would draw 6.25 amp, would use 12 gauge wire up to 50 feet, 10 gauge over 50 feet, using a 15 amp breaker,{minimum}, Hope this helps. Known wattage divided voltage gives you the amperage, voltage times amperage gives you wattage, you need to have the voltage as a known, your local electric supply will help you with wire gauge, to supply known demand, volt or wattage, Note, use separate supply breaker,

At the risk of being contrary you could go 100 feet on 16 gauge at 7 amps and be fine. Look at any of the many online extension cord calculators on the web. Home Depot has one in there Diy section of there website though there are many others out there to choose from. Nothing wrong with going bigger though. Not sure I even own a 16g ext cord. I know I have a 14 but most are 12 and and a 100 footer 10g.

I know there are all kinds of equations, how many homes and etc, burn down because of light gauge wire, have a good day;;