You will need:
- the jeans you want to hem
- your pants that are the perfect length
- iron and ironing board
- sewing machine
1. Align the crotch of your favorite jeans to the crotch of jeans that you want to hem. Notice in the pic below that when I do this, the jeans I want to hem are several inches too long.
2. Carefully cut your jeans about 1 inch longer than the length of the inseam of your favorite jeans. I usually just keep the pair of jeans on top of the jeans I am hemming while I cut, but you could also mark the length an inch past the length of your favorite jeans. This is your most important step - using a reliable length from a favorite pair of jeans to decide how much you need to cut off the bottom. If you try to wear your jeans and fold them where you want to hem them while you are wearing them, you run a big risk of making floods.
3. Turn the jeans that you want to hem inside out. Now take that inch and fold them back. Your jeans should still be inside out. Iron this area so that you have a sharp crease where you plan to hem.
4. Sew your jeans at your new length. Jeans tend to be a mustard yellow thread color, but some are white, blue, etc ... if you want your jeans to look more professionally hemmed, match the color of the thread to the thread used in other areas of your jeans. Now, simply sew down your new hem using a straight pattern. Cut off loose threads.