How does GPX differ from FIT?

GPX is a plain-text XML format for sharing tracks and waypoints. FIT (Flexible and Interoperable Data Transfer) is Garmin's compact binary format used by their devices and Connect platform. Converting lets a track recorded elsewhere be imported as a Garmin activity.

How are coordinates encoded in FIT?

FIT stores latitude and longitude as 32-bit signed semicircles, where one degree equals 2^31 / 180 semicircles. The converter multiplies each decimal degree by that factor and rounds to an integer, which is exactly how Garmin devices store position.

What fields are written?

A file_id message marks it as an activity, then one record message per track point carries timestamp, position_lat, position_long and altitude. This is the minimum a device or Garmin Connect needs to recognise and display the track.

Does the file include a valid checksum?

Yes. FIT requires a 2-byte CRC over the header and the data records, computed with Garmin's specified CRC-16 table algorithm. The tool appends the correct CRC so the file passes validation on import.

Is my GPS data uploaded?

No. The GPX is parsed and the FIT is generated entirely in your browser using the File API. Your location history never leaves your device.

GPX to FIT Converter (Garmin)

A GPX to FIT converter lets you take a track recorded in any app that exports GPX and import it into the Garmin ecosystem, which speaks the binary FIT format. This tool builds a genuine FIT activity file in your browser — no upload — so your route and timing stay private while still being recognised by Garmin devices and Connect.

How it works

FIT is a binary protocol built from a header, a sequence of records, and a trailing CRC:

File header (14 bytes): header size, protocol and profile version, the data-records length, the ASCII signature .FIT, and a CRC of the header itself.
Definition messages describe the shape of the data messages that follow — which fields, their sizes and base types.
Data messages carry the actual values. The converter writes a file_id message (type = activity) and one record message per GPX track point.
Coordinates are stored as 32-bit signed semicircles: semicircles = round(degrees × 2^31 / 180). Timestamps are seconds since the FIT epoch (1989-12-31 00:00:00 UTC), and altitude uses FIT’s scale/offset ((metres + 500) × 5).
A CRC-16 over the whole file (header + data) is appended using Garmin’s specified lookup-table algorithm.

The result is a byte-for-byte valid FIT file you can download and import.

Tips and notes

If your GPX track points lack timestamps, the converter synthesises a steadily increasing time so the activity still has a coherent timeline.
Elevation is optional; points without <ele> are written without an altitude value.
All track segments in the GPX are merged into a single record stream in document order.
The output is an activity FIT; it is intended for importing a completed track, not for live device recording.