It is important to get the right balance between bread and filling. Too much filling can make the sandwich sickly, less practical to eat, and reduce your profit margins. On the other hand, a lack of filling makes the sandwich less appetising to your customers.
The standard proportions for a sandwich are 45% of bread (110g) and 55% of filling ( 140g).
In general, the bread should represent less than 20% of the total cost price