Recently I bought a pair of jeans with a big hole in hole in the knee with the plan of turning them into capris. I didn't pay very much for the jeans so if it didn't work out how I wanted I wasn't too worried about it.
I have included a step by step instruction at the bottom of this post.
I find when I do any altering on pants that the best way to get the best and even cut is if you fold them in half with the back on the outside. After I fold them in half I take my ruler and line it up even with the outside leg of the jeans to get the right kind of cut. (seen below) **You will want to add 1" to your desired length to be able to have your hem. When you are cutting off jeans you don't want it cut straight across because then when you wear them they won't be the right shape at the bottom of the leg. When you open the pants they will have a slanted cut and that is exactly what you want, to end up with the right result.
I used a rotary cutter and cutting mat with my ruler to get the best possible cut. It works amazing. I recommend this method for a straight and quick cut. Shown below is my finished cut.
After cutting the jeans off all I did was fold it under about 1/2" and iron, then I folded it another 1/2" inch (rolled on top of the first fold), pinned the hem down and sewed my hem into the pants. I used yellow thread on the top of the hem because the thread on the rest of the jeans was yellow and I wanted it to match and look like they were made as capris.
I have repeated the instructions again for you here just in case there was any confusion.
Figure out your desired length
Fold your pants with the back facing the outside.
Using your ruler line up the line on your ruler with the outside edge of the leg on the pants.
Use a rotary cutter and mat and cut the legs off from your desired line on the ruler
Open the jeans. They will be slanted but that is what you want.
Fold the bottom hem 1/2" and iron
Fold the bottom hem another 1/2" (so rolled on top of the first fold) and iron.
Pin your hem in place and sew at desired hem height. I did mine about 3/8" seam allowance.
This was a very easy project. This project only takes about 20 minutes from start to finish. If you decide to make your own shorts, I hope you enjoy your finished shorts as much as I do.