Small shrimp (50 or more per pound) take only two or three minutes to cook. If 31 to 35 shrimp are in a pound, they need six to eight minutes of cooking time.
To boil raw shrimp in the shell, heat about 5 cups of water for each pound of shellfish. After the water comes to a rolling boil, add the shrimp and stir. Put the lid on the pot, and turn off the heat. After letting the shrimp sit for two to eight minutes, remove a shrimp and cut it in half through the thickest part. If the shellfish is opaque throughout, it is done.