During my extremely brief time as a professional seamstress in training, I spent my entire time doing one very useful, very boring, thing: hemming pants. I would estimate that approximately two thirds of the business done in a tailor's shop is hemming. Just in case anyone is harbouring a dream of opening a shop, you might want to take this in consideration.
I have never been called upon to hem a pair of pants my entire time with a sewing machine in my home (and my pre-sewing days, a staple or a bit of double sided tape usually did the trick. Don't cringe! Admire my resourcefulness :D Funtack works too!) Never called upon until two nights ago, that is, when The Man had about 2 inches too many on new pair of trousers (not made by me) he planned to wear the next day.
I apologize for the poor quality of photos. The whole procedure was done late at night (the only time anybody urgently wants something sewn) and I was tired enough to not bother to make sure I had a pretty picture. In total, though, the hemming took me less then 20 minutes, a speed I can only attribute to being forced to hem 30 pairs of pants in 4 hours. Lucky me.
How to Hem Trousers
Before any altering is done, it would be very helpful to wash and dry your trousers, to get any shrinkage out and done with before you begin.
Start with figuring out where you would like the hem to sit. With the trousers ON the wearee (put shoes on also, particularly important for high heels), fold up the bottom of the leg and determine the right length. Mark the length with a pin, woven in along where the hem should sit.
Take the trousers off. Lay them out on a table or cutting board with the legs stacked, as if you were looking at someone wearing them from the side, with the side seams all aligned (use the front creases of the pants, if there are any, as a guide to fold), bottom hems matched.
Take a good look at the hem. When a professional hems a pair of pants, they do their best to make the new hem look exactly the way the old hem did. That means using the same colour of thread and width.
For my trousers, the old hem is exactly 1".
Generally, a double fold hem is used, which means whatever hem length is desired, you will need double that number for a proper go of it. I will need 2" of material beyond the desired length for a 1" hem.
Alas, for me, there is not enough material without a little bit of extra work.
To get enough length for a new hem, usually the old hem seam has to be opened up. Professionals use a razor blade for speed and accuracy, being careful not to cut the material. A small utility or craft blade works well too. This is much MUCH faster than a seam ripper.
With the seam out, iron the trousers to smooth out the folds (which will not be perfectly flat, but that's just fine). Reposition the legs in go position, side seam aligned.
Now we have the place (still marked with a pin) that indicates our desired length, and enough trouser to make a decent hem. First up, clearly mark the desired length on the fronts and backs of both legs: With a straight edged ruler, use the raw edges of the trousers to indicate the line of the hem (this will help keep the hem shape correct, as the original design intended). Use tailor's chalk to mark the desired length.
Now move your straight edge to the other side of the line, giving you access to the bottoms of the legs.
Holding the straight edge firmly against your chalked line, fold back the top leg. Tuck the folded leg tight against the edge and hold steady. Use the chalk to mark the desired length on the insides of the legs, using the straight edge as a guide. The firmer you can hold that straight edge, the more accurate your hem will be.
Fold back the second leg in the same manner and mark the desired length of the last side.
Now that you have your desired length marked, measure down the length needed for the hem (I need 2" for my double folded hem) and either mark out where to cut:
Or just take it right off with a rotary blade (which I didn't have):
Time to sew! Turn your trousers inside out, fold back the hem and stitch hem in place using the chalked mark (desired length) as a guide.
Professionals, unless it's really finicky material, usually do not press or pin first, just have at 'er with the machine, folding in as they sew. It works quite well and makes a more accurate hem by using your fingers to fold and work with the material, rather than forcing it into a shape with a hot iron and pins. If your trousers narrow sharply, and you find that the hem will be tucked, use your razor or seam ripper to open up the side seams a bit (but do not cut up above the desired length, obviously). You can then pull the leg a bit wider as you sew and avoid tucks.
Once hemmed, press the trousers. Use a cloth over top to avoid marking or making shiny spots in the material. Plenty of steam or a direct spray of water will take out the chalk marks.
Hemming is one of those things that is so very easy (and boring, did I mention that already?) but only if you happen to have the right materials on hand. For anyone without a sewing machine, a hem is a headache. I know of several ladies who keep themselves a steady income with just hemming trousers, charging almost $20 CAN for a simple hem. Just a little bit of info to ponder :)