Determine How Much to Cut
Based on the size of the fill piece and available space for the new cabinet to meet a wall or other cabinetry, calculate the amount to cut from the fill piece. In this case, only 1/4" of a 3-1/4" fill piece was needed to make it match the other cabinetry.
Use this measurement to set the table saw. In this example, the table saw fence is set at 3" away from the blade for an accurate final dimension. Keep the table saw unplugged when not in use, especially when adjusting the distance of the fence from the blade