Many commentators understand the Hebrew word shalish to refer not to a specific measure of volume but rather to some container. The word literally means “a third.”
PSA 80:6: Here shalish may refer to a large drinking vessel. The point here is that the sorrow of God’s people is great, as indicated by the abundance of their tears. For the second line of this verse, GNT has “a large cup of tears to drink,” while NIV says “you have made them drink tears by the bowlful” (similarly CEV). TOB translates “a triple measure of tears to drink.”
ISA 40:12: Translations give a variety of interpretations to the word shalish here, including “bucket” (CEV), “cup” (GNT), “bowl” (NCV), and “basket” (NIV). However, almost all agree in using some kind of container.