The quality is judged by experts who will rank the crystals on a scale of 0 to 10. A score of 10 will be given to a perfect gem-quality crystal that fits the ideal crystal structure known for the chemical. 

1. The crystal is weighed, and the mass M recorded. It is possible to require a minimum mass, e.g. the crystal must be a minimum of 0.5 g to be eligible for judging.
2. The quality of the crystal is judged on a scale of 1 to 10, with 10 representing a perfect crystal. The following factors will be considered in judging quality: 

3. The Total Score is then determined as follows:
   Total Score = [log (M+1)] x Q
   The logarithm of the mass is chosen so that large poor quality crystals don’t swamp out smaller good quality crystals.
   
   The value 1 is added to the mass so that crystals weighing less than 1 g get a positive score.

Instead of using the Total Score to indicate the winning crystals, one can also take the amount of starting material into account.  

A 100 per cent yield crystal made from 100 g (M_t) that scores a perfect 10 on quality (Q_t) would get a theoretical maximum of: 

[log (100+1)] x 10 = 20.01 

The actual score can also be expressed as a percentage of the maximum. The crystal with the highest Overall Score is then the winning crystal. 

100 x {[log (M+1)] x Q} / {[log (M_t+1)] x Q_t} = Overall Score % 

For example, the best overall crystal in the  Canadian 2001 contest with 150 g starting material weighed 46.53 g and had a quality of 8.65. Its overall score was: 

100 x {[log (46.53+1)] x 8.65} / {[log (150+1)] x 10} = 66.6%

This score is nearly an absolute score that could be used to judge different types of crystals grown from differing amounts of starting material.