How to find the better buy of two of the same item, but they have different units of measurements and different costs.?

First, you can convert the measurement units with probably online or by simple calculations. For example, Orange juice A is 2 L, meanwhile Orange juice B is 200 millilitres. From 1 L = 100mL, we can conclude that juice A has 2L and B has 0.2L. 
now both are at the same unit. to the cost, we can simply calculate the cost for the same for example 1L by multiplying or dividing the cost. In the same example, given that juice A costs $11, and B $2.
cost for juice B if its 1L = 2 x 1/0.2
= 10
Therefore, we can conclude that juice B is a better buy because $10 is cheaper than $11 when both are at 1L rate.

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is