TCX to FIT Activity Converter

Convert TCX to FIT when you have a Training Center XML activity and need a binary activity-file representation for a supported workflow. This TCX to FIT converter accepts one running, biking or other activity with lap summaries and ordered trackpoints, then writes FIT record, lap, session and activity messages. Available GPS, elevation, distance, heart rate and cadence are mapped. You can review the summary and download activity.fit, while keeping the original because extended measurements and device-specific information are not all transferred.

What the TCX to FIT converter produces

TCX expresses an activity as XML elements. FIT uses binary messages and field definitions instead. A conversion must write a coherent activity, not merely replace the filename extension. This TCX to FIT converter emits the common message structure and file checksums for the supported activity profile, using a locally bundled FIT encoder.

The resulting file is a generic activity export. It does not pretend to be the original recording from a particular watch or bike computer. A receiver may still expect fields, manufacturer behavior or upload rules beyond the supported mapping. Independent decoding is part of the implementation’s verification, but an actual device or training-platform import has not been tested here.

Choose an activity and inspect the conversion

1. Select Choose file and open one .tcx activity export. The example control loads a small supported activity file.
2. Wait for local processing, or select Process files if you need to rerun the current input.
3. Check the displayed sport, lap count, record count and total distance against your source export.
4. Download activity.fit, retain the .tcx original and test a small import in the destination application.

There is no control to pick an arbitrary output sport or manufacture missing sensors. Running, Biking and Other values are read from the accepted source activity. A multi-activity export should be separated in the source application before using this TCX to FIT converter; the supported input is one activity, not a library archive.

Example: two measured trackpoints

Consider a lap containing points at 09:00:00Z and 09:00:05Z, each with valid coordinates. The second point has a cumulative distance of 20 meters, a heart rate of 125 and a cadence of 80. When the lap summary supplies compatible start and duration information, those common measurements can be encoded as FIT records alongside the lap and session summaries.

A 20-meter cumulative distance is stored as activity distance, not the straight-line geographic separation invented by the TCX to FIT converter. If the source does not contain a heart-rate measurement for a point, the conversion does not guess one from pace or an adjacent record. Compare the summary as well as the route so that a plausible-looking line does not hide missing activity measurements.

Fields transferred and fields left behind

The supported mapping includes GPS positions, elevation, cumulative distance, heart rate and cadence where they are available and valid in the TCX source. Ordered timestamps identify the sequence of records. Required lap summaries provide activity organization; they are not inferred from an arbitrary list of coordinates.

Calories, power extensions, courses, structured workouts and proprietary extension fields are not mapped. A TCX document describing a course or workout is therefore not interchangeable with a recorded activity. If you need a navigable route rather than the activity container, FIT to GPX conversion is a different workflow and also loses activity-specific information.

When the source needs attention

Malformed XML, multiple activities, unsupported sport values, missing lap information, invalid coordinates or out-of-order timestamps can stop conversion. Re-export from the original recording application when possible. Do not sort XML lines manually: element order, lap ownership and the meaning of cumulative values all matter.

For a damaged GPX route that you already extracted, GPX file repair can remove impossible track points conservatively, but it cannot reconstruct a missing TCX lap summary or restore power fields. Keep a record of which format changes were made instead of treating successive exports as equivalent copies.

Validate the receiving workflow

The Garmin FIT activity documentation explains how recorded activities differ from other FIT file types. Check your destination’s current upload policy separately. A valid binary decode is evidence about file structure, not a promise of acceptance by every platform.

All activity bytes are processed in the browser, without signing into a training account or sending the file to a conversion API. The download is a new file; the source remains available for comparison. Verify lap boundaries, elapsed time, route position and retained sensor data before relying on the converted activity for analysis or sharing it.

Common TCX to FIT converter errors and how to fix them

When the TCX to FIT converter cannot use a file, it stops with one clear message instead of producing a half-finished download. These are the problems people run into most often, with the fix for each:

• Use one supported TCX activity with valid lap summaries and ordered trackpoints. The file has no activity or several, a lap lacks total time or distance, or trackpoints are missing.
• A GPS timestamp is invalid. Trackpoint times go backwards, are before 1990 or are not ISO dates.
• A GPS coordinate or elevation is invalid. A latitude or longitude is out of range.

Privacy: the TCX to FIT converter runs in your browser

TCX to FIT converter processing happens with JavaScript in a background worker on this page. Your file is not uploaded to a FileFix server, and the results you download are created in your browser’s memory. Activity and location files reveal where you live, train and travel, so they are worth keeping on your own device. When you finish on a shared computer, clear the selection or close the tab.

For the underlying format rules, see the Garmin FIT SDK overview. The TCX to FIT converter follows the subset described on this page rather than every optional feature in those documents.

Sources

• Garmin FIT activity documentation
• Garmin FIT SDK overview

Questions about this tool