Record the measurement. See the attached worksheet for assistance. If you have a pair of pants that fit you well, you can measure those also. I appreciate having your actual measurements but finished measurements are important. Lay your trousers on a flat surface - dining room tables work well and floors work well.
Place inseams together.
Lay the trousers flat. Measure from the top of the waistband to the bottom of the cuff. Record the measurement. With the trousers laying flat from your previous measurement, fold back the top leg to expose the inseam. Measure from the crotch to the hem.