Put on the trousers and mark the desired hem length with pins or chalk
Remove the trousers and measure the hem allowance evenly around both legs
Turn the trousers inside out
Cut off excess fabric if needed, leaving enough allowance for a hem
Fold the raw edge up to the marked hem line
Press the fold flat with an iron
Fold the edge up again to create the hem depth
Pin the hem in place all the way around each leg
Thread a needle with matching thread and knot the end
Use small hand stitches such as a blind stitch or slip stitch
Sew around the hem, catching only a few threads from the outside fabric
Keep stitches even and secure
Tie off the thread when finished
Repeat for the other leg
Press the finished hem flat with an iron