Accurately cutting baseboard molding to fit tightly against door casings is a bit tricky. To avoid costly mistakes, make a simple marking gauge. Cut a piece of ¾-in. plywood about 3 in. wide and 4 in. or so taller than the baseboard. Next, saw a notch into the edge of the plywood block equal to the height and thickness of the baseboard. Now, set the baseboard molding in place against the wall, allowing it to run past the door casing. Place the notch in the marking gauge over the molding and slide it tight against the casing. Draw a pencil line along the face of the gauge and onto the molding. Cut the molding to length on the line for a perfect fit—every time.