The general rule for selecting a crawfish pot is 2 quarts of water per pound of crawfish, so the best size crawfish pot depends on how much crawfish you plan to cook. A 60 quart pot can handle a 30 lb sack of crawfish, an 80 quart pot can handle a 40 lb sack, and so on.
Typical crawfish sacks range from 28-42 lbs, so an 80 quart pot is ideal for handling a typical sack. But don't worry if you have a smaller pot, just split the crawfish in half and boil in two batches.
Also many people boil everything from potatoes, corn, sausage, garlic, lemons, onions, mushrooms, even brussel sprouts with the crawfish, so depending on your extras you might need a larger pot.
Another thing to consider is the soaking time, while crawfish only need to boil for 2 minutes, most people allow them to soak for 15 to 30 minutes. This means each batch will take 40 minutes to an hour depending on soak time and time to boil. The time it takes to bring your water to a boil is a factor of pot size and burner BTU. For the fastest boil times try one of our double jet burners.
With a smaller crawfish pot you are limited to the amount of crawfish that can be cooked, but you can heat and cool a smaller pot faster. I find that the 80qt pot is the best size for boiling an entire sack of crawfish.