Use 'glassful' to describe exact amounts, suggesting you have a whole glass of something.

Quantity Specific

Remember, 'glassful' is only for liquids. Don't use it for solids or powders.

Not for Solids

'Glassful' implies the glass container is filled to the top, not partially full.

Whole Container

 The number of molecules per glassful is hugely greater than the number of glassfuls, or bladdersful, in the world. And of course, there's nothing special about Cromwell or bladders -- you have just breathed in a nitrogen atom that passed through the right lung of the third iguanodon