How many have you got? Oh, and then maybe divide that by 3.
The first point to make is that individual eyelash extensions are all added to the upper eyelid only. (It is physically possible to add extensions to the lower lashes, but they would be very short and sparse, because there’s not much there to work with. There are fewer lashes, and you can only extend a lash by 50% so it doesn’t make much difference.)
The average upper eyelid apparently may contain anywhere from 90 to 160 eyelashes. (Personally, I object to referring to anything as the average when you then go on to say ‘anywhere from 90 to 160’. That’s not an average. However …)
Yes, thank you … However, you are never going to have as many extensions as that, even with a ‘full set’. Not all your lashes are suitable, or available, for carrying eyelash extensions. Your eyelashes all go through a natural process of growing, reaching maturity, and falling out, and being replaced by new ones.
Eyelashes which are in the ‘anagen phase’, as it is called, which is basically their first two weeks of life, cannot support the weight of eyelash extension. They would just make the lash break or fall out. It is only lashes in what are known as the ‘catagen phase’ or ‘the telogen phase’ which can support extensions. (The ‘catagen phase’ is the period when the lash is still growing but is already strong enough to support an extension. The ‘telogen phase’ is when the eyelash is fully-grown and mature, and can definitely support an extension.) As a result of all this, the number of extensions which can be added to an eye may vary from person to person, and from time to time.
The number of individual lash extensions you will want to add to an eye depends, to a large extent, on the effect the you want to achieve. For what is known as the natural look, 30 to 35 eyelashes may be about right. For a full-on glamour look, intended for a party or event, then the number might be raised to 40 to 60 eyelash extensions per eye.