Some bottles have markings, some dont. And some of the 90ml ones have "space" for extra liquids. To avoid wastage and defrosting too much, what i do is simply to use a permanent marker to roughly mark every 30ml level (which is about about 1 ounce) so 3 markings per bottle. (Most nurseries/infant centres feed in increments of 1 ounce or 30 ml eg 90, 120, 150, 180, 210 and if you use formula, they also use 1 spoon of powder for 30ml of water. So the 1 ounce/30ml measurement is a nice simple guage for long term use. Happy storing.