The volume of the liquid tank provided in the design of the atomizer. Note that this parameter can be specified even for squonk atomizers (see "Filling type"): although they work with an external tank, however, a certain amount of "liquid" can fit in the evaporator itself.
The larger the tank, the more liquid you can keep in an electronic cigarette and the less often you have to refill it. On the other hand, capacious tanks have the appropriate dimensions, and too large a tank would be inconvenient, and liquids are consumed relatively little even in one long session of soaring. As a result, a volume
of more than 6 mL is already considered quite large for vapes, and in the smallest models this figure
does not exceed 2 mL.
Also note that when choosing a tank capacity, manufacturers usually take into account the resistance of the spiral, the power of the battery (if it is included) and other parameters that affect the expected flow rate of the liquid. There is no hard dependency here, however, in general, more powerful atomizers are usually equipped with larger tanks.