The old rule was that you could measure them at 2-years-old and double the height to find out their likely adult height.
But now there are several websites with reliable growth charts that take a lot more detail into consideration.
I went to About.com which is reviewed by the Medical Review Board and seems easy enough to navigate. You can plot the information about your newborn, or any age child up to 20-years-old. And there's a section for you to read about on growth spurts. When they typically happen and how to take it into consideration when you're trying to assess height and weight.
First let's talk about those growth spurts. It may seem like your newborn is growing at a steady pace, a half ounce heavier per day...but what if he or she has a few days with no weight gain? Then your baby gains several ounces at once. Should you worry? Most pediatricians say "no." You should look at the average weight gain for your newborn over a one-month period. For the typical 3-month-old, it's about one and a half to 2 lbs. a month.
There are some variables, like whether the baby is breastfed or bottle-fed.
And it depends how many feedings the child has. Do they eat every 2 hours or every 3? Should you "feed on demand" giving them as much as they seem to crave? Or should you have a set limit? Again, check with your pediatrician. But many doctors suggest a feed-on-demand schedule but a basic total intake at the end of the day. So it's less important if your baby takes 3 ounces in the morning, but then guzzles a full bottle in the afternoon. As long as they are regularly taking a bottle or being breast fed, it tends to even out.
The growth charts themselves are quite interesting. There's one that plots the typical length and weight for boys from birth to 3 years...and from girls birth to 3 years. Then there's a separate chart for children age 2 to 20, broken into boys and girls. There's also a body mass index chart so you can take into consideration whether the child seems to be a slim build or full-sized.
If you have questions, of course ask your pediatrician. This website isn't written in stone. But it's meant to be a way to gauge growth for the curious parent.