The chapter states, 'When you want to mention the quantity of an uncountable item, you should use some measure words before it. For example, 'a tube of', 'a bar of' and 'a bottle of' are measure words.'
Class 6 › English Grammar and Composition › Chapter 1: Parts of Speech › Topic: Countable and Uncountable Nouns (Measure words)
Aligned to the NCTB national curriculum.