The short answer: Google Maps doesn’t use much mobile data at all when navigating. In our experiments, it’s about 5 MB per hour of driving. Most of Google Maps data use is incurred when initially searching for the destination and charting a course (which you can do on Wi-Fi). There are ways to ensure Google Maps doesn’t use any mobile data at all when driving.
So, Google Maps only doesn’t need much data to get you where you need to go. That’s good news; for how useful the service is, you might expect it to use much more than the miserly 5 MB per hour.
You’ll note we said navigation; if you pull over en route to search Google Maps for, say, somewhere to go for lunch, you’re obviously going to be using more than the approximate 5 MB per hour. However, if you’ve downloaded an area map for offline use, you can perform this search without using any mobile data. It’s a useful and relatively recent addition to Google Maps.
There are ways to ensure Google Maps uses even less data than that, though.
Downloading Google Maps so you can use them offline on your phone is easy. We’ve outlined the steps in Download Google Maps for offline use blog post. You can download a map for offline use on both Android (as outlined in the link above) and on iPhone.
If you decide to use Google Maps offline, there are some sacrifices. While you can search for nearby establishments or points of interest, the information you see will only be as recent as the last data you downloaded. Things like holiday hours may not be accounted for, as an example. If you decide to deny Google Maps access to mobile data at all, you won’t have access to traffic or other real-time road information. Finally, you can only get driving directions when operating Google Maps offline. As it stands, cyclists, transit users or pedestrians need not apply.