Why can you use the technique of measuring volume as a means of counting?

You can use measuring volume to count how much of something there is. Such as if you know that a jar has a volume of 200 mL, and you need to put 400 mL of salt in a recipe, then you know to have 2 jars full of salt. So it can be a way to effectively measure large amounts of substances while also helping out practically. Hope this helps!