There is no exact or standard amount of cheese to use. Most home pizza makers just eyeball it and use experience as a guide. Many professional operators do pre-portion cheese, however, because it is one of their biggest cost components, and especially recently where cheese prices have been high. There is software out there that estimates amounts of cheese (and other ingredients) to use for different sizes of pizzas and one such piece of software (Food Cost Pro) suggests 6.5 oz. for 12-inch, 9 oz. for 14-inch, and 12 oz. for 16-inch. If you have a heavier hand and cost is not an issue or you feel that it is worth it from a competitive business standpoint, you can add 1 oz. to each of those numbers (that is what Big Dave at PMQ did when he was on the operating side of the business). If you are an operator and trying to cut back on costs (which some do when cheese prices are high), then you can cut back an ounce or more for the three sizes mentioned. Those who pre-portion usually weigh the cheese or use measuring cups geared to this purpose.