My ponytail vary several milimeters in thickness up and down between times I measure.

[Venefica]

I get obsessive over thickness so I measure it not like all the time but perhaps once or twice a month and I have discovered that my around the ponytail measurement go up and down and up again, some times it s 10 cm, then it go up to 10,3 or even 10,5 and then it go down again, and then up again far faster than it would take to loose and regrow hair. This makes me a bit puzzled do anyone know why this is. I usually always measure on clean but dry hair.

[Pinkster8]

I noticed the same thing- my hair goes between 2.75 inches and 3 inches between measurings... I think it may be due to when I last washed my hair, and how long it's dried.

[torrilin]

Mine ranges from 2.5" to 3", so about 1cm of variation. I don't really worry about it, since it's not like hair is super uniform, always free from static, always in the same humidity, always with the same amount of leave in, always the same level of cleanliness... I'm positive there's other stuff that plays in too, like what style I had it in last, whether there are any coating ingredients or build up in my hair...

In short, it'd be really tough to set up consistent enough conditions that the measure would always be the same. Variations happen when we measure things. Part of learning to measure well is learning to believe in the variations and just record them. Sometimes it's your ability to measure that's wonky, but more often you're measuring a real change.

[CharleaMurphy]

Maybe your ponytail isn't always as tight...

[nightwish90]

do you use the same kind of string or measuring tape? maybe the tapes/strings don't extend the same way when you keep them tight around your hair

[spidermom]

I think you're just looking for an average anyway. I don't measure very often, but have gotten slightly below 4 inches and slight above. I think it depends on how fluffy my hair is. Today it's uber-fluffy and I would probably get the biggest measure yet (but I don't care).

[jeanniet]

I don't measure circumference often, but I've seen mine vary by more than half an inch. I think some of it has to do with how tight the measurement is, because even a slight variation is going to make a difference, but also whether the hair is freshly washed, etc. There's quite an increase in volume if I measure after washing with standard shampoo and conditioner (which I don't do much), although I'm not sure why.

[cooklaezo13]

My measurement varies so much that I'm not even sure if I'm a ii thickness or a iii thickness. When my hair is down it looks incredibly thick, so maybe I am more like iii? Not sure. I think it varies because of how tight I make the ponytail and whether I am holding the string I use to measure at an angle. It can also vary by humidity, oiliness of the hair (or lack thereof), etc.
Also at this length, I have a lot of short pieces that just barely reach into my ponytail. My ponytail measurement changes depending on how careful I am about getting all of my hair actually into the ponytail.
I wouldn't worry much about it unless you feel you are shedding more hair than what is normal for you.

[Vanilla]

I have the same problem. Sometimes I measure my ponytail and it's 3.5 inches, and sometimes it's 3.75 inches. If its super fluffy, then I may measure 4 inches.

[Quahatundightu]

I counter this by always measuring my circumference after my hair has been freshly washed and dried. It keeps the curl pattern more or less the same and I seem to get pretty consistent results.

[auburntressed]

My pony has been known to jump around about 1/2" in thickness, so I just say 5" as that is what is most average and in the middle of what I get. I've noticed it is always thickest right after being freshly washed and dried, and always thinnest when it gets dirty/greasy/weighed down by sebum or leave in oils. Coincidentally, it is also heaviest when it is the "thinnest." My pigtails measured individually always add up to more than my pony tail taken all together, too, by about an inch.

[Venefica]

I use the same type of hair ties every time I measure and I usually always have my ponytail tight as it is so smooth that if I do not the ponytail holder will fall off the hair. I also always measure with newly washed dry hair so it have the same conditions.

Do you guys by the way measure over or under the hair elastic when you measure thickness?