Not so important tutorial, but since some of my friends asked me how. I thought I'll just make a tutorial out of it.
Start with, wear the pants and fold the pipe to the length that you want

Mark it with sewing pin

Take the pants off :P

Measure the folding part, here is 7,5 cm

Mark 4 cm from the folding side, of course this is depends on how long the pants is originally, what kind of model etc.

Open the fold and put few sewing pins to make sure that it won't move when you cut it

Cut it

Fold the pipe 4 cm

Iron it

Folded half inside so you got 2 cm measurement

Iron it again

Put on the sewing pins so it wont move during sewing

Sew it

Cut the excess thread

Finish!!!

A happy customer :)