Trousers rarely come from the manufacturer in exactly the right length, but you can adjust the length of men's dress trousers by hemming them. Wear the shoes you will be wearing with the trousers, and adjust the marking pins as many times as needed to get them straight. The trousers legs will ride up when you bend over to pin them, so set the pin right where you want the trousers leg to fall, stand up and see if it is where you want the bottom edge to fall. Try again if it is in the wrong spot.
Measure 1½ inches out from the straight pins used to mark the desired length, using the seam gauge or ruler. This is going to be the length used when cutting off the excess fabric. Mark the cutting line with straight pins. If you do not have enough fabric to leave a 1½-inch hemline, keep the fold line pinned for now.
Cut off the excess fabric using the scissors, removing the bottom layer of pins as you cut, then use the sewing machine to sew all the way around the leg's raw edge. Use either a zigzag or over-lock stitch to finish the raw edge.
Fold the hemline under using the remaining pins as a guide. Pin the folds one inch above the fold-line, in four places. Pin each side seam as well as the centre front and center back. Remove the fold-line pins.
Iron the folded hemline to flatten it and to set the fold.
Poke the needle inside the top edge of the hemline at one of the side seams. Move the needle straight up and catch two or three threads from the side seam. Move 3/8 of an inch to the right and catch two or three threads in the centre of the finishing stitches on the hem's raw edge. Move 3/8 of an inch to the right again, and pick up two or three threads with the needle's point, just above the hemline. This is called catch stitching. Repeat the catch stitching until the hem is finished, then repeat on the other leg. Remove the remaining pins.