Estimating your terminal length

First of all, I want to point out as other people have before, that “terminal length” isn’t as much about the length added, but about the time it takes a hair to complete its growth-resting-shedding cycle. Since this cycle is genetically preset and hard to change and that every single follicle has its own cycle-length and growth rate, the most descriptive and correct term would actually be:
“Terminal time”
Terminal length is simply the result we experience from the terminal growing time.

Some of the people reading this, will now be thinking “But I have only ever grown my hair to armpit/shoulder/BSL length so my terminal length is super short!”

Stop. Right. There.

No.

If you go on a hair forum as a new member, you have not tried everything. You have not tried oils, alternative washing methods, supplements, benign neglect and so on. The list is long. You can find more tips and help than you can imagine if you start with the forum's stickies, work through the articles and use the search function to find the good threads packed with information. Even long-term members who thought they reached terminal length long ago can grow longer with different handling and routines.

Now for the calculation-part…

There are a couple of different ways to estimate your terminal length. One method is based on the taper of your ponytail and the other is based on your shedding rate

For the first method you put your hair in a low ponytail and put elastics around the length every 10-15 cm all the way down. Then you measure the distance from the first elastic at the neck to each of the elastics and plot it in on a graph. Call that X
Now you measure the circumference of the ponytail on each of the elastics and plot that in too. That is your Y

The points should give you a somewhat linear graph and if you do it by hand or a program you can extend it and estimate where the circumference reaches zero. This is your estimated terminal length using the taper calculations.

Keep in mind that any layers you have will massively impact the resulting line and give you a false, low terminal length.

Another method is that you take the estimated number of hairs on your scalp and divide it with your annual estimated shedding (Daily shedding x 365) that number is the number of years it will take for your scalp to have replaced all the hairs growing.
Multiply this number with your annual growth (monthly growth x 12 or total growth as some people have higher growth in the summer)
This is your estimated terminal length using the shedding calculations

The average number of hairs on your head:
80,000 for redheads
100,000 for brunettes/black hair
120,000 for blondes

(Estimated number of hairs on your head) / (Annual estimated shedding) = Years to have replaced the hairs on your head

(Years to have replaced the hairs on your head) x (Annual growth) = Estimated terminal length

Of course this will never be completely accurate because:

• The shedding method will show a big difference if you add or subtract just 10 hairs
• Breakage and trims are not included
• Some hairs have a longer growth cycle than others
• Terminal length can fluctuate over the years due to hormones, stress and diet
• You don’t know exactly how many hairs you have on your head

If you get a completely crazy number out you know cant be true, don’t forget how big a difference different numbers input makes. If you don’t believe that, try changing the numbers just a little bit.
The math isn’t wrong.
The numbers we put in however will always only be an approximation of real life.
Shedding 45 hairs instead of 50 makes a big difference. Putting 90,000 hairs on your head instead of 100,000 makes a big difference too. And the annoying thing is, you will most likely never know these real numbers for sure.

Here is an example using my own numbers 

I think I’m more brunette than blonde, but I have an unusual amount of hair for my heritage, so let’s say I have 120,000 hairs on my head anyways. 

I’d say I lose about 50 hairs a day.
I actually counted them a couple of times during the years! Can you believe that?! 

I must have been seriously, incredibly bored. But hey, now I appreciate the work I did then.  

That makes my annual shedding 50 x 365 = 18,250 (Yikes!)  

So 120,000 / 18,250 = 6,57 

This means, that according to my calculations, I should run out of hairs in the growth cycle on my head in a little over 6½ year.  

Now for the growth: 

I get an unimpressive 1,5 cm per month with 2-3 months in the summer with 2 cm. 

Let’s say (12 x 1,5) + (2 x 0,5)  = 19 cm 

That’s fairly accurate too. I have a few years during my growing out where I didn’t trim at all and I got 18,5 cm length gain in total for the year.  

Now we do the final step: 

6,57 x 19 = 124,83 cm.  

Placing a measuring tape at my neck, 125 cm lands me a bit below knee length. Doesn’t seem too far off, I think?

Explanation of terminal length
Like no two snowflakes being alike, no two hairs grow to the same length. People have short hairs that never grow to the full length of the rest, usually around the hairline and temples (Personally I have two sets of “donkey ears” of the thickness of a pencil that only grow to ear to brushing shoulder length) That is completely normal.

When a hair comes to the end of its natural growth-cycle, it will enter a resting phase before being ejected from the follicle. This means that a single hair will be at its absolute maximum length for a relatively short period of time. In the meantime, the vast majority of hairs from the scalp will be at varying lengths in the process of growing out.

If you practise S&D, you will snip individual ends to get rid of damage, but it shouldn’t influence your hemline much. The general shape of your hemline won’t change even if you snip ½ inch from individual hairs and it definitely shouldn’t shorten your possible length.
That means that hair reaching the maximum length will be heavily tapered. Members who have reached their true, untrimmed terminal length often describes their very tippy ends as “The few, longest trailing hairs”. That is maybe the best description of what true terminal length will look like.

This picture shows what actually happens during the growth-cycle:

However, don’t pay attention to “3-6 years”. This is a number being thrown out there frequently, but so far there hasn’t been much evidence of the “normal” terminal growth time. Basically, no one has done any real, true studies about what the human maximum hair growth is. It seems to be one of those numbers that people pull out their sleeves “Because everyone knows that!” on the line with such “knowledge” that normal shedding is 50 hairs a day.
Being on a hair forum will show you that such things simply aren’t true.

Link to a simple calculator:
http://www.allvidzhaze.com/phptest/hairgrowth.html