Impossible question to ask if you are new to
vaping, use different devices throughout the day or know how much you normally vape during a normal. Under prime conditions, you would vape a single flavor all day long and determine the nubmer of ml's you consume over a period of time to determine how much
e-liquid you need to have each month.
If you are constantly testing flavors, switching flavors during the day, using different devices, or using different nicotine concetration juices, it is nearly impossible determine useage. I understand that 2ml - 4 ml is about an average. Hell, if I smoke my DSE601 pipe for a whole day, I would likely vape through 5-10ml of liquid very easily.