Take off the pants. Carefully turn them inside out without disturbing your pins. 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. Use this measurement to fold and pin the rest of the hem. Measure in at least in four places all the way around to make sure it is even. Use chalk to mark each measurement. Do not use pen, pencil or markers, because they can stain and even run after washing. Measuring correctly now means less to adjust later. Measure, fold and pin the other leg in the same manner.
Now you are ready to iron the hem.
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