The total quantity of overhang in an undermount sink varies, but average measurements are 1/4 or 1/8 inch over the rim of this sink. Having this amount of countertop stretching beyond the rim is typically known as favorable overhang. Professional installers occasionally create positive overhangs as much as 3/8 inch.
Factors in deciding the quantity of overhang include personal design preferences, the size of the sink and the setup directions from the sink manufacturer. Positive overhangs allow good drainage of fluid and food debris from the countertop to the sink, while also addressing setup hardware and caulk lines used to seal around the outside of the sink. In case a brand new sink is installed later on, the favorable overhang provides some leeway in deciding upon the size of this replacing sink.