Trim around a jamb is typically referred to as door casing.

How to measure jamb depth. Use a tape measure to measure the height of the window from top to bottom in three different places. Do it at the top, middle and bottom of the jambs to get three width measurements. The result is your door opening depth.

Standard door casing is typically 2 1/4 inch wide, and about 5/8 inch thick. Make note of the largest of the three measurements just in case the. Measure the depth of the door frame, or jamb.