How much data am I using on a two hour ride? If it matters I am in good service the whole time.

I can't imagine it's all that much. Have you tried looking at your cellphone bill?

It is not that much. I have a 5 yr old Samsung. In settings you can check data usage by app. May not even be granular enough, but you can check usage by Strava before and after a ride and see if there's much difference.

It simply can't be much. There just isn't that much data to send. The max would likely be the size of the Fit File that was produced. Look at that and I'd guess that would be the amount of data you sent.

That's a good starting point for an estimate, but the size of the fit file is a floor, I would say. Although it depends on what level of strava you have. The other stuff is probably not much though. I'm thinking of live segments. Are there other features where strava might send data?

Strava does download maps as one rides, depending on the screen one is on.

I think much of what it does is when one completes the segment (at home by WIFI?). Every time it seems to download maps and recent segments by oneself, and one's followers. Uploading a completed segment always seems to be unbelievably slow.

It might be interesting to do an experiment of traveling with Strava enabled, and having it off, and looking at the data use logs. I agree, probably not that significant, a few megs, at least if one starts/stops while connected to WIFI, and perhaps keeps it off the mapping screens.

Your phone should have a window for mobile data usage under the settings icon.

Since August 25 my Android phone has used 5.5MB for Strava and 3.55MB for Wahoo Fitness -- I run both. That's six rides of 20-40 miles, mostly continuous, ranging up to 5-6 hours of use.

For an entire month's use from July-August, Strava used 23MB, Wahoo Fitness used 10MB. That's several rides a week, 100-150 miles a week.

Cycling apps are among the lowest drains on my monthly data plans -- 3 GB per month on my Android phone, 1 GB/mo on my iPhone. By far the biggest data drains are Facebook, Chrome, Google, YouTube and news apps I check a lot. Even my mail and weather apps are minor drains.

Features like Strava Beacon and other realtime tracking features and apps would drain more data. I haven't used those.

I used a Hammerhead Karoo for a year, which had an internal SIM card so it would upload ride data without being tethered to a cellphone. It averaged about 1MB per ride. I don't see why a .fit file from a Strava app would be any larger.

I don't watch much video on my phone, so Pandora accounts for a full half of all of my data usage.

If you want to limit data you can also run Strava in Airplane mode and upload file once the activity is done.
Obviously you miss some of the features already noted here like live segments (who does that anyway?), Beacon and map updates.

I checked the data usage for one ride just by resetting my usage. I didn't think of that until reading some replies. A one hour and thirty-six minute ride - a regular ride I do - used 336 KB. The ride started and ended on the Wi-Fi where I am staying.