Fat content of Mozz?

[sierracheese]

How does one determine the fat content of finished mozzarella made with 4.5% fat milk?

Started with 5 liters (5100 grams) milk and ended up with 620 grams mozz at the end of the cheesemaking process.

Is the only way to get an accurate reading to send it to a laboratory for testing? Or is there some formula I can use?