How to join GPX files
- Get every track. You need one GPX file for each stretch of the outing. If you don't have them yet, the export guide covers the apps that make them, for instance Strava, Komoot and Apple Watch.
- Drop them above. Once they're in, each file gets a row with its own start and distance, the map shows where they lie, and a figure for the whole outing appears. Files that overlap, or that are far apart, get a message here.
- Choose the format and save. The picker starts on FIT. Switch it to GPX if that's what your next app wants.
Your files aren't sent to any server; the tab does the work itself.
Recorded tracks only, not planned routes
"GPX" covers two different things. One is a track, which a phone or watch wrote while you moved, with a clock reading on every point. The other is a planned route: a line somebody drew, or a file you loaded to follow, with places but no times.
FitMerge joins the first kind. A file without times is turned away with the message has no times. It looks like a planned route, not a recorded activity. If you want to chain planned routes into one longer line, a route editor is the right tool, because there is no moment to place each part at.
What the GPX reader takes
From each track point it reads the time, the position and the elevation. From the point's extensions it reads heart rate, cadence, power, speed and temperature, under the extension names that Garmin's and Strava's files use. Distance isn't stored in a GPX file, so it is worked out from the positions. A GPX also has no moving time, so that is estimated from your speed, and the stats table says so.
Data a file doesn't have simply stays empty. Averages use only the points that carry a value, so a part from a phone with no heart-rate strap doesn't pull the average down to zero.
Times and time zones
A GPX time normally ends in Z, which means UTC, and then there is nothing to guess. Some apps write the local
clock instead, with no time zone at all. FitMerge reads such a time as local time at the first GPS point of the file. Without
GPS it can't tell where you were, so it falls back to UTC.
This matters when you mix sources. Say a watch file is in UTC and the phone file is in local time. If both were read the same way, one part would shift by hours, so the parts could overlap or show a gap that isn't there. Reading by place puts them back next to each other. We tried a track moved to Shanghai, with one part written in local time and one in UTC, and the two parts joined cleanly.
Sport
A GPX can say what you were doing in its type field. FitMerge understands the names Strava, Garmin Connect and
several other apps write, such as walking, running, hiking and the older number
1 for a ride. If the file says nothing, it follows the other part. If none of the files says, the page asks you
to pick the sport in a box above the download button and won't save until you do. The choice matters: a walk read as a ride
gets a different idea of when you stopped.
Which format to save
GPX has no laps, and the page notes that laps, pauses and calories are lost when you save one. The merged GPX keeps each part as its own track segment. FIT and TCX keep each part as a lap. A GPX has no distance field, so Strava, and FitMerge itself when it reads one back, add up the points, including the straight line across the gap between parts. On our test ride Strava showed 81.69 km for the GPX and 81.65 km for the TCX.
If the merged file is headed for Strava or Garmin Connect, pick FIT: Garmin Connect doesn't read the
type above, and files a GPX as Other. Our test is told in
the Garmin Connect guide, and the Strava side is in
its own guide.
Questions
I only have routes, with no times. Can I join them?
Not here. The page needs the time of each point to know which part came first and how long you stopped, and a planned route doesn't carry any. The file is rejected with a message that says so, and the others you added are still read.
Do both files need to come from the same app?
No. We merged a Strava GPX with a Garmin Connect GPX, and a bike computer's FIT with a Strava GPX of the same ride, and both worked. FIT and TCX files can join GPX ones too, and a FIT part supplies the device. Make sure they cover different minutes, because two files that cover the same time are refused.
Does the merged GPX keep my power?
Yes. Heart rate, cadence, power and temperature are all written into the track points. What a GPX can't hold is laps, pauses and calories, so FIT is the better choice if you want those.
Why is my GPX total a little longer than the FIT?
Strava, and FitMerge itself when it reads a GPX back, measure a straight line from where one part ends to where the next begins. In our test the FIT and TCX of the same ride, 81.65 km, don't count that gap.