Things You'll Need
Wood or circular saw
Polyurethane or wood glue
Stain or paint
A door cut too short is not difficult to open or close, but it is an eye sore, and it allows anyone to peer underneath. Before cutting a door to size, it is important to accurately determine how tall the door should be. If the door wasn't accurately measured, you can extend its length. There could be, however, some mismatch in the grain pattern or color when the door is extended, which may require that you restain or paint the door.
Measure the gap between the floor and the door.
Push the pins out of the door hinges with the edge of a flathead screwdriver and remove the door from the frame. Lay the door on a flat work surface or saw horses.
Measure the width of the door.
Find a filler piece of wood or composite with a similar look or grain pattern. If possible use the scrap that was cut from the original door.
Cut the filler piece 1/2 to 1 inch shorter than the gap between the floor and door with a wood or circular saw. Cut the filler piece so it is the same width as the door.
Drill four clearance holes all the way through the filler piece.
Stick the filler strip to the bottom of the door with polyurethane or yellow wood glue. Wipe off any excess glue with a rag.
Hold the filler piece to the door with a clamp until the glue dries.
Drill pilot holes with an electrical drill or Phillips screwdriver through the clearance holes. Drive the screws through the clearance holes.
Stain or paint the filler piece to match the door if necessary. When staining, apply it with a rag. Allow the first coat to dry before applying a second coat. When painting, apply primer to the filler piece with a paint brush before the paint. In some cases, you will need to paint or stain the entire door again so the filler piece matches the rest of the door.