Measure the width of the window opening with a tape measure.
Transfer the measurements to the window shade and make a mark with a pencil where you will need to cut the blind.
Roll out the blind and place it on a flat surface, such as the floor or a workbench.
Use a tape measure to measure the amount of the fabric shade that needs to be cut off of one end.
Make two to three marks down the length of the shade with a pencil.
Place the straight edge over the marks you made and cut the fabric along the straight edge with a utility knife.
Close the shade and cut the end of the head rail and valance, if necessary, with a hacksaw along the cut end of the fabric shade.
Remove the cap from the small end of the blind with pliers and then place the cap on the end of the newly cut shade.
Mount the shade in the window to complete the project.