What is the formula for calculating volume of a hexagonal container? I need to make a coontainer that will hold 300ml and it must be a hexagon. Thks

The volume is

\frac{3\sqrt3}{2}s^2h \;\approx \;2.6s^2h,

where s is the length of one of the six sides, and h is the height.

Also, for what it's worth, the maximum diameter of a hexagon (the distance across from vertex to vertex) is twice the length of a side, or 2s.

Hence, to hold 300ml (a.k.a. 300 cubic centimeters), you could use, for example, sides of length 4 cm (i.e. a diameter of 8 cm). That would result in a required height of just over 7.2 cm (because 2.6\;\times\;4^2\;\times\;7.2=299.52\; \text{cm}^3).