Clamp a metal straightedge, such as a framing square, along the line to be cut.

Apply a strip of masking tape along the line to protect the finish and reduce splintering.

Draw the cutting line on the front and edges with a pencil.

Use a blanket (or other padding) to cover your cutting surface, typically a sawhorse.

Pull out the hinge pins on the door.

Mark the clearance needed on the door. Allow for a 1/4-inch to 1/2-inch gap.

Determine whether your door is solid or hollow. Hollow doors require an additional step, since the bottom may end up being cut off.

Cut along the line with a utility knife to score the door. Cut through the tape and into the door. Make a few passes.

Use a circular saw or hand saw. Make sure the saw blade is sharp and has at least 18 teeth.

Remove the metal straightedge.

Clamp a straight 1x4 or 1x6 board to the door to act as guide for the saw. Position the board so the blade will cut about 1/32-inch to the outside of the cutting line.

Guide the saw along the board to trim down the door.

Remove the clamp, board and masking tape.

Hang the door. Swing it completely open and closed on its hinges. If the door still rubs against the floor, lay a pencil flat on the floor and run the tip along the face to mark a line.