GPX ViewGPX, KML, TCX, FIT: which format for what?
Four extensions circle the same track, and the choice is never a matter of taste: each one carries things the others cannot describe. Here is what each holds, and what survives a conversion.
GPX, the exchange format
This is the common one, the format almost everything reads. Tagged text, legible as it stands in an editor: a list of coordinates, sometimes with an elevation and a time of passage. It carries no colour, no photo, no sensor reading — and that bareness is exactly what makes it universal. When a device or a site accepts one format only, it is nearly always this one.
KML, the format of globes
KML describes shapes laid on a map, with their styling: colours, icons, layers, folders. It is what globe software asks for, and all it asks for. Its standard line describes a geometry, not a journey through time: it has nowhere to put the hour a point was reached. KMZ is not a fifth format, merely a compressed KML — and it happens to be the export offered by default.
TCX, the training format
TCX is tagged text as well, but it was designed for a session rather than for a path: it carries timestamps, laps, and sensor readings — heart rate, cadence, power. It is what many watches produce on export. It is markedly heavier than a GPX for the same outing, since it describes a great deal more.
FIT, the binary of watches
FIT is not text: it is a binary file, compact, unreadable by eye and impossible to correct by hand. That is what makes it frugal — a long outing fits in a few hundred kilobytes — and also why it takes a decoder to get anything out of it. It holds the track, the time and the sensors, and even tells the stopwatch's pauses apart.
What a conversion leaves behind
Converting never loses the track, but it rarely loses nothing. Towards KML the timestamps go: the format has nowhere to put them. From KML it is the styling that goes, which GPX cannot describe. From a TCX or a FIT, the track, the elevations and the times come through — the sensor readings do not, for want of anywhere to hold them in an ordinary GPX. Converting one way and back does not hand you the original file: always keep it.
Telling what you are holding
- A .gpx file
- Open it in a text editor: you should read tags and coordinates in plain sight. It is the safest format to hand to a device, to a site, or to someone else.
- A .kml file
- Text as well, but arranged into folders and styles. It nearly always comes from globe software, and that is where it goes back. For a GPS it needs converting.
- A .kmz file
- An archive holding a KML, sometimes alongside images. No need to unpack it: the converter on this site opens it as it stands and fetches the KML inside.
- A .tcx file
- Text, often several times heavier than a GPX for the same outing. If it is refused somewhere, a GPX is what is being asked for: the conversion keeps the track, the elevations and the times.
- A .fit file
- Opened in an editor it shows nothing but unreadable characters — that is normal, it is binary. It has to be decoded to become a GPX; this site does that in the tab, with nothing sent anywhere.
Convert your file
The converter on this site works out the direction from the file you drop in: a GPX comes back as KML for globe software, a KML or a KMZ comes back as GPX for a GPS. Watches have their own pages — TCX and FIT to GPX — listed at the tools hub. Everything happens in your browser, with no account and no upload, and each page states on screen what its conversion cannot carry.
Frequently asked questions
- Which format should I give a GPS or a hiking app?
- GPX, almost without exception. It is the only one everything reads, and it is the one the other three convert into.
- Why does my file grow when it becomes a GPX?
- Because a FIT is binary and a GPX is text: the same points are written as readable digits rather than packed bytes. What the file actually holds does not change.
- Can I get back to the original file after a conversion?
- No. Whatever a format cannot describe is lost at the first conversion, and retracing your steps does not bring it back. Keep the original next to the converted file.
- Is KMZ a different format from KML?
- No, it is a compressed KML, sometimes alongside images. The converter on this site opens it directly, with nothing for you to unpack.