There are several different types of "5mL" bottles out in the wild. Two main types are most common in my exp. The first is the soft plastic:
These will hold slightly more than 5ml, but not 6ml.
The other bottle I've seen is not child proof, and is advertised as a 6ml bottle:
These bottles will hold just over 6ml. TPA uses these for their DIY flavors, as does DIY superstore. I've received both kinds in random numbers, whenever I order 5ml samples of juice.
The only way to know for certain would be to measure, most easily done with a decent syringe (no needle needed). Just use an empty bottle and fill it with water using the syringe, will tell you the capacity (close enuf anyways).
ETA: if you are nearby any kind of drugstore, walgreens, wal-mart pharmacy, or even a tractor supply store, you can get plain syringes for 20-30cents each. All I have found are in sterile individual packages (even a TSC).
Scoring them free is also excellent if you have the sources!
