If you have a lot of split ends, your hair will seem thinner since you don't have as many hair strands that reach to the ends.  

One gauge for hair thickness is to measure the circumference of the ponytail. If you have bangs and/or you can't get all of your hair in there adjust according to how much of your hair you have measured.

thin (less than 2 inches/5 centimeters)
normal (between 2-4 inches or 5-10 centimeters)
thick (more than 4 inches/10 centimeters)

Do you feel you are shedding a lot?  Do you lose a lot of hair when you comb or brush your hair?  If so and your doctor feels you are healthy (did they check your thyroid?), you might consider adding MSM, Biotin, and Silica supplements.  I have found these have minimized shedding significantly.

Trimming small (1/4") amounts at a time, will help to even up the length without sacrificing the length.  Split ends should always be trimmed.

It doesn't sound like your hair is very thin, at least not based on your ponytail.  

To find split ends, look at the ends of your hair.  If you see the hair make a "Y", it is split.  If you look at the shaft of the hair for as much of the length as you can see, look for a white "bump" on the shaft.  This would be a spot where the hair has partially broken and will soon break off.

To trim for splits, use a very sharp scissors.  Take a section of hair and gently  twist it into a rope.  Ends will stick out of the rope.  Look at these ends and trim any that have splits.  This type of trimming is frequently called "dusting".  When you are done, you might have a dusting of hair on the table/floor.  

To minimize the frizzies, you might want to try some jojoba oil on the hair from ears down.  A very small amount of oil is used ( 1 - 3 drops should be enough).  I usually put a drop of oil in the palm of my hand, rub my hands together, then slide my hands down my hair, spending more time/oil on the ends.  I repeat this until I have oiled all the sections of my hair.  A good time to oil your hair is before you go to bed.  Oil the hair, then braid or bun your hair.  By morning your hair will have absorbed the oil and should look shinier (but not oily).  

If you haven't done so already, I'd suggest you read through the Ultimate Guide to Growing Long Hair listed under the site features at this site.

Can you tell us more about your hair care routine?  What products do you use?  Do you use any heated appliances (hair dryer, curling iron, straightener, etc)?

Poor KatharineAnn 

The splits you are finding halfway up... you should still trim them off just above the split.  When you don't, the split can catch on other hair and cause tangles.  It might take a while to find them all, but be patient and trim them as often as you can.  I will look for splits when talking on the phone, watching TV, whatever.  Just be sure to have sharp scissors and good light - you don't want to cut the wrong hair!

Since you like your current length, you could trim the total length by the amount of growth you have.  The average hair growth is 1/2" per month.  You might want to try to measure your growth then plan on trimming that

Your hair is the most vulnerable when it is wet.  Brushes will pull your hair more than combs.  When wet hair is pulled or stretched, it can cause breakage.  Try this routine on the weekend and see how it works for you:  Wash and condition your hair.  Do not pile your hair on top of your head, instead, massage the shampoo and conditioner down the length of your hair.  When rinsing the conditioner out, gently run a wide toothed comb or hair pick through your hair to remove tangles.  Squeeze the excess water out of your hair.  If you use a leave in conditioner, put it on the length of your hair.  Wrap your hair in a towel and leave it in the towel for 15 - 30 minutes. Take the towel down and either finger comb or use the wide toothed comb again to remove any tangles.  If you must use the hair dryer, try to use it on the low setting and don't dry your hair bone dry with the dryer. 

This routine will put less stress on the hair which will help minimize damage which is what can make your hair feel frizzy or unmanageable.  It might take a while for your hair to show the improvements if it currently has a lot of damage.  You might look for a deep moisturinzing treatment for your hair to help repair some of the damage you already have.  Jojoba oil at night can also help restore lost moisture due to previous damage.

Once your hair is long enough to pull around to the front easily, you can trim your own hair.  I know what you mean about salons.......I've had my share of bad experiences.  My husband is the only person who trims my hair.  One thing we used to do to make sure he trimmed it straight, was for me to wear a shirt with horizontal stripes.  He could use the stripes as a guideline for making sure it was even.  I usually have him spray my hair just enough to make it damp and therefore a bit easier to keep the hair straighter for cutting.  I've heard of some gals going to a barber shop instead of a salon.  Barbers tend to charge less and concentrate more on doing just the basic cut that you ask for.  Talking with the person first to make sure they understand exactly what you want and how important it is for you to keep the length on your hair, should improve your odds in getting just a trim.

I hope this helps a bit.

It's so depressing to read about the ponytail diameter thing.  Even with my bangs  in there I would never even have 1 inch.

Is there anyone out there with hair as thin as mine?

Thanks for the reply and the suggestions.  I suppose I've seen those things.  I'll have to look around.

The lady I work with has several times the hair I have, but she's always complaining about it.  Seems people never appreicate what they've always had.

Thanks.  I will look.