What is the adult dosage for Miralax ?

It's on the bottle. Turn the cap upside down, fill the white part with the powder, mix thoroughly in 6-8oz of water. Once a day, no more than 7-days.

There is a line around the inside of the large purple cap, you fill it to that line. That is 17g. Then pour it into 4-8 oz of water. You do that once a day until you get results. The directions are on the label.