I don't know the measurement of Ionic jets bt suspect that they are 3mm or maybe more. I seem to get through more water when I use them but I've never measured it scientifically. Also, I changed to microbore around the same time as starting to use other jets so that may have affected water usage too. The Ionics jets seem OK but I'm not convinced. For instance, if the leisure battery starts to run low, it does seem as though a fuller stream of water is needed that appears to be provided by narrower jets. But like Dave says, there can be a splashback factor. Another issue is that when using narrower jets, there is an occasional blockage that needs sorting out. I've never had a blockage with wider jets. So a few pros and cons I think.