Pops are a 5:1 ratio. The colder and more carbonated your water the less syrup you'll use. Experiment with the number of pumps to find the amount that suits your taste.
4L of syrup makes approximately 67-78 cans of pop depending how you drink it sweet or light and bubbly.
Thinking of shipping syrup? Max out the box with 8L of syrup for the best value.
DON'T FORGET YOUR SYRUP PUMP!