Whether it is men's or women's trousers, few of us are a perfect "off-the-rack" size. It can be expensive to have them altered every time you purchase a new pair of trousers. Shortening your own trousers can be done easily with just basic sewing skills. A second person is helpful to help you mark that first measurement at the hem level, while you have them on.
Put the trousers on. If you normally wear a belt with them, put it on. Also, slip on the shoes you usually wear with the trousers. Standing erect, have another person mark the trousers, with a straight pin, where the hem should be on each bottom leg. Remove the trousers.
Measure and mark where you will put the hem, plus an additional 1 inch, around both bottom trouser legs. Cut the excess fabric off.
Sew a zigzag stitch (or serge stitch) around the edge of each bottom trouser leg, using matching thread.
Pin the hem at 1 inch to match the marked hem from Step 1, using straight pins.
Sew close to the edge of the zigzag stitch, with matching thread, for casual trousers, such as jeans. For dressier trousers, hand sew the hem on each leg with a slip stitch. Press the new hem with your iron to make a crease.
A quick way to hem trousers, although not as permanent, is to purchase an iron-on hemming tape, such as Stitchwichery, at a fabric store. It is a fabric adhesive that is ironed on, sticking to both sides of the fabric on a hem.