Here's how to hem up a pair of pants so they keep the original look but are the right length. By cutting the pant leg above the original hem line, you can keep the original hem of the jeans you bought. Measure carefullly to remove the excess length of pant that you will not need. This process will only work if you need to shorten your pants by at least one inch. You need one half inch seam allowance to re-attach the original hem onto your newly shortened pair of pants.