Adjusting the length of a pair of pants is the most common clothing alteration. Hems can be adjusted by hand stitching, by sewing with a machine, or by using hemming tape that is melted with a warm iron to glue the material together.
This page explains how to hem using a sewing machine that can do blind stitching. Many sewing machines costing less than $100 Dollars have this capability. In addition to the sewing machine, you will need scissors, a seam ripper, thread matching the color of the material, a tape measure, an iron, and an ironing board. It also can help to have purpose-built tools, such as a fabric cutter made by Fiskars. You can recover the cost of your sewing equipment after just a few alterations when you consider the money that you would pay for professional alterations.
Determine the correct length. Fold the excess length of the pant cuffs toward the inside of the pant leg and pin the pants to the appropriate length. When measuring, it is important to take into consideration the kind of shoes that will be worn with the pants. The jeans illustrated here are fitted for use with high heel shoes, and they will probably be too long to be used with sneakers or tennis shoes. If you measure with tennis shoes, the pants will be too short with high heel shoes. Body posture also affects the measurements. Make sure that the person is facing straight and not looking down when the measurement is taken. Pin the pant cuffs at the proper length or mark the pants with a small mark of taylor's chalk.
Turn pants inside out without disturbing the pins or the chalk mark. With your measuring tape, find the length from the bottom fold to the top edge of the fabric that you folded up and inside the leg.
Iron the hem. Still working with the pants inside out, iron the hems to make a crease at the correct length. Keep measuring as you position the pant legs for ironing to make sure that the length is uniform.
Trim the pants. Be sure that you have measured properly before cutting. If you cut too much you may spoil the garment. Keep the pants inside out. Extend the pants to their full length and trim them depending on the type of hem: For a simple straight hem (e.g. jeans or pant lining), trim about one or two inches below the crease. For a blind stitch hem (e.g., dress pants), trim about two to three inches below the crease.
Start sewing. Load your bobbin and top spool with the same color of thread. The thread should match as closely as possible the original thread used on the pants.
For a simple hem with straight stitching, set your machine for a small to medium straight stitch. In this picture, notice that the stitch width lever is set to the extreme left position. Fold the hem so that the cut edge is folded in toward the crease. Begin stitching 1/8 inch from the top of the hem and go all the way round.
Straight stitching is used for jeans or for the lining of dress pants. The seam side of pant linings normally faces the seam side of the pants so that the interior and the exterior of the pants both present the finished side. Pant linings are usually sewn with the pants right side out, but with the pant leg gathered toward the crotch so that the lining extends enough for sewing.
For blind stitching, set the stitch width and the stitch pattern to the correct position. Here, the stitch width lever has been set to the middle position.
A machine blind stitch consists of three or four straight stitches that sew the inside hem followed by a sideway stitch that attaches the inside hem to the pant leg by just a thread. This picture shows a sewing machine that uses a cam and dial to select the sewing pattern. For cam number 1, the dial has to be set at position B to select the blind stitch which is illustrated in gray color on the side of the machine under the letter B. Read the instruction manual for your own sewing machine to determine how to select the stitch pattern.
Sewing the blind hem stitch. Working with the pants inside out, fold the hem so that the cut edge is folded toward the crease as for the straight hem, but then fold the final edge toward the inside of the cuff leaving 1/8 inch to start sewing. The following photographs illustrate the technique for folding the material
Folding the material for a blind hem stitch. This photograph shows how the cut end of the pants cuff is folded toward the inside of the ironed crease, and then the pant leg is folded once more leaving a 1/8 inch offset for machine blind stitching. For some materials, it may be necessary to iron the fold toward the inside of the previously ironed crease to make the sewing easier and more accurate.
The material is in position for blind stitching. Notice that the inner seam is offset about 1/8 inch to the right of the fold in the pant leg.
The blind stitch. This illustration shows the blind stitch in contrasting colors. For every four straight stitches in the inner seam there is a sideways stitch that attaches the inner seam to the pant leg. The width of the stitch determines the distance of the sideways stitch from the straight stitches. You must choose the appropriate stitch width to barely catch the material. If the stitch width is too large, the finished side will show big stitches, whereas if the stitch width is too narrow, the sideways stitches will not catch the pant leg.
View of the reverse side of blind stitched hem when it is unfolded for final ironing. This is the side that will face the inside (toward the legs) when the pants are worn.
Front side (finished side) of blind stitched hem. Once the material is ironed, the small stitches are virtually invisible when thread that matches the color of the material is used.