Fitness File Converter

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.

The Four Fitness File Formats Explained

Fitness devices and apps use four main file formats to store and exchange workout data. Understanding what each format contains — and what it drops — helps you pick the right conversion for your workflow.

FIT — the richest format

FIT (Flexible and Interoperable Data Transfer) is a compact binary format developed by Garmin and widely adopted across devices from Wahoo, Suunto, and Polar. Because it is binary, file sizes are small even for long activities. A single FIT file can hold GPS coordinates, altitude, heart rate, cadence, power, temperature, ground contact time, vertical oscillation, stride length, and hundreds of manufacturer-defined developer fields. It also preserves lap boundaries, session metadata, and device configuration — making it the only format that carries the full picture of a workout.

TCX — structured XML with heart rate and laps

Training Center XML (TCX) was introduced by Garmin alongside the Training Center desktop app. It is a human-readable XML format that retains most core metrics: GPS coordinates, altitude, heart rate, cadence, power, and calories. Crucially, TCX preserves lap structure, which makes it the preferred import format for platforms like Polar Flow, Fitbit, and older Garmin software that do not accept FIT directly. TCX drops advanced running dynamics (ground contact time, vertical oscillation) and any device-specific developer fields found in FIT.

GPX — universal GPS exchange

GPX (GPS Exchange Format) is an open XML standard maintained by Topografix and supported by virtually every mapping application — Strava, Komoot, Wikiloc, Google Maps, and most route planners. Its core elements are waypoints, routes, and tracks, each carrying latitude, longitude, elevation, and timestamp. Heart rate, cadence, and power can be added via Garmin's TrackPointExtension schema, but many apps that accept GPX simply ignore these extension fields. If you need to share a route or visualize a track, GPX is the widest-compatibility choice — but expect to lose lap data and advanced metrics.

CSV — flat data for analysis

CSV (Comma-Separated Values) is not a fitness format per se — it is a plain-text table. Each row represents one data point (typically one second or one GPS fix), and columns hold every metric captured at that moment: timestamp, latitude, longitude, altitude, heart rate, cadence, power, speed, and more. CSV carries the raw numbers but loses all structure: there are no laps, no session boundaries, and no hierarchical relationships. CSV is ideal for importing into Excel, Google Sheets, Python pandas, or R for custom analysis, chart building, or research.

Which Conversion Should You Use?

The right conversion depends on what you want to do with the file. Here is a practical decision guide:

• Uploading to Strava or a mapping app: convert FIT or TCX to GPX. GPS and elevation data are all you need.
• Importing to Polar Flow, Fitbit, or an older Garmin product: use FIT to TCX to keep heart rate, cadence, and lap data intact.
• Building a custom spreadsheet, chart, or running your own data analysis: convert to CSV. Any source format works — FIT to CSV gives the most columns.
• Archiving or re-uploading to Garmin Connect: keep the original FIT file. No conversion needed. Garmin Connect only accepts FIT for activity import.
• Sharing a planned route (no activity data): GPX is the universal standard. Export to GPX and load it into any route-planning app.

Data Retention at a Glance

The table below shows which fields survive each conversion. A tick means the field is fully preserved; a dash means it is dropped or unreliably included.

Rule of thumb: convert toward the simplest format you actually need. Going FIT → TCX → GPX drops progressively more fields. Always keep your original FIT or TCX file — conversion creates a copy and never modifies the source.

Common Conversion Mistakes to Avoid

• Converting GPX back to FIT expecting to recover lost data. GPX does not store heart rate or power in a standard way, so a GPX-to-FIT round-trip will produce a file with GPS and elevation only — the same data the GPX held.
• Uploading a converted GPX to Garmin Connect. Garmin Connect does not accept GPX file uploads for activity import — only FIT files work. If your goal is Garmin Connect, keep the original.
• Discarding the original file. Always keep the source FIT or TCX. Conversions are lossy and irreversible in one direction; the original is your only backup.
• Assuming extension fields in GPX will be read. Many apps accept GPX but only parse the core spec (lat/lon/elevation/time). Heart rate and cadence stored as Garmin extensions may silently disappear.

Frequently Asked Questions