The Price Per Square Foot field is not one of the default fields on the search screen, but you can use the Additional Fields section at the bottom of the search screen to add it to the search. There are actually several different variations to choose from:
The orange highlighted fields are based on the listing's Total square feet. If the list agent has entered data in the Heated Below Grade Square Feet field (in addition to the Heated Above Grade Square Feet field) during input, that is part of the Total Square Feet of the property and will be factored into the price per square foot calculation.
The pink highlighted fields are based on the listing's Above Grade square feet.