Different rats will eat different amounts of food and the amount a rat eats will vary over the course of their lives. Generally, rats eat a total of around 15 to 25 grams of food per day, each. If you're choosing to portion out their food, I'd suggest starting by giving them a total of around 17-18 grams a day and then pay close attention to how long the food is lasting them and be sure to weigh them regularly to ensure they're gaining, losing, or maintaining their weight appropriately. You'd want to adjust how much you're giving daily depending on these factors.
As for proportions, I do around 70% primary diet and 30% vegetables/fresh/wet food. As for treats, I keep it to a minimum. I might give them 1 baby puff a day or let them have a quick nibble of whatever I'm eating.
The Isamu Rat Care youtube channel has a great playlist called [
"Feeding Rats"] that has loads of information about diet and weight.
