Convert FIT (device activity file) to KML

Be clear about what this conversion is for: KML is a geometry format built for Google Earth and similar viewers, not a fitness format, so turning a FIT file into KML gives you a route you can fly through and view against real terrain, and nothing else. Heart rate, cadence, power, temperature, and distance all get dropped in the process — not because of a limitation in this tool, but because KML's specification never included a place to put sensor data in the first place. What does carry over is time, latitude, longitude, and elevation, which is exactly what a 3D flyover needs. One detail trips people up if they've hand-edited KML before or compared it against another format: coordinates in KML are written longitude, latitude, elevation, the reverse order of GPX, TCX, and CSV, which all put latitude first. This tool handles that ordering automatically, so the output opens correctly in Google Earth without any manual fixing. There's no lap structure in the result either, since KML has no lap concept any more than it has a sensor-data concept. If what you actually need is to preserve your heart rate and power numbers alongside the route, this isn't the right target — CSV, TCX, or GeoJSON will keep that data — but if the goal is simply to see the shape of a climb or a course laid over satellite imagery and terrain, KML is the simplest path there. As with every conversion on this site, the FIT file is read and the KML written entirely inside your browser, in a background worker, so nothing about your route is sent to a server, and the tool is free for files up to 25 MB, three at a time.