This is a handy reference to have when using liquid crab boil such as Zatarain's to boil seafood, any seafood. Zatarain's also has a Lemon flavored and Garlic and Onion Flavored liquid crab boil.

Amounts below are calculated by quantity of water used. The problem I've found with the directions on the label is it tells you how much liquid to use for X amount of pounds of seafood, not how much water you use. Seasoning intensity is dictated by the seasoning to water ratio. 

Water    -   Crab Boil

1 Gallon - 3 1/3 Tbs.

2 Gallons - Just under a 1/2 cup

3 Gallons - Just over 1/2 cup

4 Gallons - Just over 3/4 cup

5 Gallons - 1 cup

Remember, these are estimates. If you like a little more spice add a little more crab boil.

When I use liquid crab boil I like to add a little black pepper, granulated garlic and maybe some lemon and pepper seasoning.

Bagged crab boil is great, but, you must remember that to draw the seasonings out you should boil then simmer the bags at least 30 minutes.