[header] How to cook corned beef in a crockpot [title] Shop for a brisket at your local supermarket or butcher's shop. [title] Choose a brisket that is about 3 to 4 lbs. [step] ( 1.3 to 1.8 kg). 
This size will fit well in most slow cookers. If you have a smaller slow cooker, you may need to cut your brisket into a manageable size.