Here is my quick way for hemming jeans. I've tried many ways, and have been using this method for the past 10 years. Beware this is a long post... Simple technique, but many pictures.
First set up your sewing machine to do a straight stitch. I use a stitch length of 3.0 and a heavier needle. A jeans needle or topstitch needle if you have one.
Next, measure your jeans. For my husband, I have him stand on the floor in his sock feet and I pin up the jeans 1 inch above the floor. Then lay the jeans out on the ironing board and fold up the other leg so both are even. Iron up the hemline on both legs. Give a really good pressssssss... I use steam too... See the line it makes. This is a good guide.
Next, cut about 1 inch down from the pressed line. I just eyeball it. But measure if you must. Set aside the bottom of the pantleg for a recycle project.
Next take small snips about half an inch long, on either side of the bulky seams. Total of 4 slits on each leg.
Next, tuck in the raw edge of the hem so it is folded in so that your one inch of hem is now about a half an inch. Leave the thick seam sticking up. Do not fold it under.
Pin all around. Notice that I pin with the heads of the pins sticking towards me, so I can easily remove them as I sew.
Next, using ORANGE thread in the top and bobbin, sew near the top of tucked in fold all around the hem. In the early days, I was matchy matchy and used light blue thread. It looked awful. Orange is the color to use. Unless, the jeans you are hemming were originally hemmed with a different color like white. I would use that as a guideline.
Stitch right over the seams. Most sewing machines don't have trouble with two layers of seams.
Snip off the portion of the seam that is sticking out.
Your jeans are hemmed. Since it's the bobbin thread that shows on the outside hem of the jeans, I keep a bobbin of bright orange thread in my bobbin caddy at all times. I primarily use it only for jeans and I think I've been using the same bobbin for 5 years. If I had the 10 years of hemming jeans back, I think I would have found a heavier weight of orange thread and used that in my bobbin. When this bobbin runs out , I will refill with a heavier orange thread.
After Note: Denise left a comment that Joanns carrys Jeans thread. You can bet this will be on my list the next time I go to Joanns. Thanks Denise.