FIT vs GPX vs TCX

Every device and platform offers some mix of these three, and they are not interchangeable. Here is what each one holds and when to reach for it.

FIT

FIT is Garmin's format, and now the industry's. It's a compact binary file: a header, a stream of typed messages, and a checksum. A record message every second holds position, heart rate, power, cadence, speed, temperature, and whatever else the device knows. Around that sit lap messages, a session summary, device info, and a growing list of extras such as running dynamics, cycling dynamics, and training effect.

Because it's binary, a FIT file is small and fast to write, which is why devices record in it. Because it's typed and versioned, it holds far more than the other two. The cost is that you can't open it in a text editor, and a damaged file needs a real parser to recover.

Use FIT for uploading to Strava, Garmin Connect, TrainingPeaks, or Intervals.icu. It carries the most data and platforms trust it. Export the original FIT whenever you're going to edit, merge, or repair an activity. There's a fuller reference to the FIT format on this site.

GPX

GPX is an XML text format for GPS tracks, routes, and waypoints. The core spec knows latitude, longitude, elevation, and time, and nothing else. Heart rate and cadence can be attached as extensions, and most devices do that, but there's no standard for laps, power, or a session summary, and each vendor's extensions differ.

It's human-readable, universally supported, and the right choice for anything about the shape of a route rather than the effort.

Use GPX for planning and sharing routes, loading a course onto a device, importing a track into mapping software, or moving a recording somewhere that only understands tracks. Don't expect laps or power to survive.

TCX

TCX is Garmin's older XML format, from the Training Center days. It sits between the other two: it has laps, heart rate, cadence, and a per-lap summary as standard, and power through an extension. It's verbose, so files are large, and nothing new has been added to it in years.

Use TCX when an old platform or tool wants it, or when you need laps and heart rate in a readable text file. Otherwise it's a fallback.

Which one to export from Strava or Garmin Connect

• Export Original on both platforms gives you the file the device uploaded, usually FIT. This is the one to keep.
• Export GPX gives you the track. Fine for maps and route sharing, lossy for everything else.
• Export TCX exists on Strava and is mostly there for older tools.

Converting between them

Going from FIT to GPX or TCX loses data but is easy: Strava and Garmin Connect both do it from the activity page. Going the other way, from GPX to FIT, has to invent what's missing, and tools that do it (GOTOES is the well-known one) produce a file that uploads but won't have laps or sensor data that was never there.

FIT File Editor opens and writes FIT only. The comparison of FIT tools lists which of the others handle conversions.