This question makes no sense. Measuring cups by definition are used to measure a standard, agreed-upon measurement. That measurement could not have been agreed upon unless someone had a cup which held that amount, or was marked off to show that amount. Once you have one, you can make a million.
Unless you’re asking how people measured ingredients for recipes before they had standards for measurements. I presume they had to test proportions (5 horns of black pepper to 1 1/2 conch shells of baking soda) until they found something that worked, which is the same thing they do nowadays.