A great thumb rule that I wish I'd seen (or noticed) long ago: Start from the easy to remember value for AWG 10 at 1 ohm per 1000 feet, the other gauges are all sized in dB. AWG 20 is 10/1000, 24 is 25/1000,
16 is 4/1000, 0 is 0.1/1000 and so on. The "real" numbers vary by manufacturer and specific part numbers, of course, but the thumb rule comes in handy for estimating.