Outside of personal preference, it is recommended that your farmhouse sink be 3 inches smaller than the size of the base cabinet you are considering installing. For example, the generally recommended size for a 36" farmhouse base cabinet is a 33" farmhouse sink or smaller.
Please note: A farmhouse sink will require a farmhouse base cabinet (not a standard kitchen cabinet) or one made custom for the sink by using it as a template.
Always check the product specification of the sink you are interested in to see the manufacturer recommended base cabinet size. Also, do review the installation guide.