This instructable assumes that you understand basic sewing concepts.
Sewing tools required:
-scissors (good sewing scissors that can cut denim),
-a straight edge ruler
-marking tool (tailors chalk, or sewing marker - a regular pencil/pen can work too)
-sewing machine with heavy duty needle (size 16, 18 or a denim needle)
Step 1: Determine Desired Length
I have turned the extra fabric to the inside. I placed a pin at the outside and inside seams of each leg to mark the length I want. Be sure you do this to both pant legs.
Take the jeans off. At this point you need to determine the line you will cut to shorten the jeans. Lay the pants out flat. Compare the insides of each leg. If your pins aren't exactly aligned, place a new pin half way between the original pin on both pant legs to find the average desired length.
Compare the outside leg seams in the same way, adjusting the pins to find the average.
Step 2: Mark and Cut
I used a thin line of tailors chalk to mark between the pins. I placed a straight edge up to the pins and drew a line between them on the front and the back of the pant leg. This will be the line you cut.
Remove the pins.
Now it is time to cut! You want to cut one thickness at a time so I started by making a little cut on the line to make a hole to put the bottom blade of my scissors through. Cut on the line to remove the bottom part of the pant leg.
Step 3: Prepare the Old Hem to Be Re-used
On jeans that have had special finishes applied (like 98% of the jeans available) there is typically a dark line just above the original hem. Use your chalk (or whatever marking tool you have) to draw a line 1/2 inch above that dark line. That dark line will help to hide the seam where you join the old hem to the pants.
Cut this line in the same way you did in the last step.
Now you need to pull out the old stitching of the hem. I've included two different seam ripping techniques.
First way - pick the stitches from the top. Use the tip of the seam ripper to go under each of the stitches to pull them out.
Second way - On the wrong side (inside), pull the seam apart. Use the seam ripper to help separate the threads.
Seam rip the entire hem.
Step 4: Reattach the Hem
I've laid the pant leg and hem out so you can see how the pieces need to be aligned to sew together. You want to sew right sides together matching the inseam and the outseam. Pin the pieces into place.
What thread should you use? You can get denim thread at most fabric stores. I usually use an all-purpose thread in a color that matches the thread I took out. It's your choice.
At your sewing machine (with a heavy duty needle - 16, 18, or denim needle), you want to sew the two pieces together at a 1/2 inch seam allowance.
Note: When you sew over the inseam or the outseam you are sewing through a lot of layers of denim. If your machine struggles to get over that much fabric, it helps to take place some folded up scrap fabric behind the needle under the presser foot. The scrap fabric levels out the presser foot so it can handle the thickness of the fabric better.
Now you need to iron it. For the best finish you want to press the seam open first to lock the stitches in place. Then, press both layers of fabric down so the cut edges will be hidden under the hem.
Step 5: Sew the Hem
At this point, fold the hem to the inside so it looks like it did way back at the beginning before you took a seam ripper to it. Make sure you tuck the cut edges of your seam inside the hem so they don't show when you look at the inside of the pant leg.
At your sewing machine, top stitch through all the layers to secure the hem in place. Follow the original sewing line with your line of stitching.
That's it! Now your pants are short enough you don't walk on them!