Understanding Data Loss in Conversion
File conversion between fitness formats is inherently lossy when moving from richer to simpler formats. FIT files are the most data-rich — they store heart rate, cadence, power, temperature, ground contact time, vertical oscillation, and hundreds of developer fields. TCX retains most core metrics (GPS, HR, cadence, power) but drops advanced running dynamics and device-specific fields. GPX is primarily a GPS format — it stores coordinates, elevation, and timestamps, but heart rate, cadence, and power are only included as non-standard extensions that many apps ignore. CSV flattens everything into rows and columns, preserving the data values but losing the hierarchical structure (laps, sessions, events). The conversion direction matters: FIT → TCX loses running dynamics; TCX → GPX loses lap structure and possibly HR data; GPX → CSV is nearly lossless since both are simple formats. Always keep your original files — conversion creates a copy, never modifies the source. This tool processes everything in your browser, so your data never leaves your device.
How to Convert Fitness Files Online — Free & Private
Whether you train with a Garmin watch, a Wahoo head unit, or a Suunto device, your workouts are stored in proprietary file formats. This free converter suite lets you move data between platforms without uploading anything to a server.
What is a FIT file?
The Flexible and Interoperable Data Transfer (FIT) protocol is a binary format developed by Garmin. It stores GPS, heart rate, cadence, power, and hundreds of other fields. FIT files offer the richest data but aren't supported by all platforms.
FIT vs GPX vs TCX — which format to use?
- FIT — best for storage and analysis. Richest data. Required for Garmin Connect import.
- GPX — best for sharing routes. Widely supported by Strava, Komoot, Google Maps, and mapping apps.
- TCX — best for heart rate and cadence across older platforms like Polar Flow and Fitbit.
- CSV — best for data science, custom charts, and spreadsheet analysis.
Is my data safe?
Yes. All conversion logic runs as JavaScript in your browser tab. Your fitness files are never uploaded to any server. The converted file is generated locally and downloaded directly to your device.