Most standard trim is 2-4 inches wide so you can include it in sqft measurements. However, some homes have trim and baseboards as wide as 6 inches.
For a more precise wall sqft measurement, subtract the width of the trim or baseboard from your totals. So for a 9-ft wall with 6-inch baseboards, subtract 6 inches to get 8.5 vertical feet of wall space total. Multiply the length of the wall by 8.5-ft to get the total square footage.