When our real estate agent calculated the sale price for our home she used?

comps from recent sales in the area but she only multiplied the first floor sq ft by that number. The second floor of the house was multiplied by 1/2 that dollar per sq ft. Is this the correct way to set a fair price? The house is actually 1 1/2 story but we used actual interior wall to wall measurments to get accurate totals.