Vertical blind slats attach to a headrail mounted over a window frame. If you have a previously used blind and you want to reuse it, in some cases, to get the vertical blind to fit over the window properly, you must trim the slats to shorten the blind. Some vertical blinds use wooden slats, others use plastic and some use metal. Different tools are used to trim the slats, but the overall process for each material is the same.
Measure the distance between the floor and the bottom edge of the headrail mounting location with a tape measure. Subtract 1 inch for floor clearance. This is the your slat length.
Measure from the bottom of the slat to the bottom of the headrail with the tape measure. Subtract the total in step one from the total slat length. The difference is the amount of slat to be removed.
Measure up from the bottom of each slat to the measurement obtained in step two and mark.
Place a contractor's square against the edge of each slat, line up the straight edge with the mark and scribe a line across the face of each slat with a marker.
Trim the slat to length. If the slats are wood, trim them with a coping saw and then sand the edges with sandpaper to smooth them out. If the slats are metal, use a pair of tin snips to cut them. If the slats are plastic, use sharp scissors to cut them.