What is a FIT file?

A FIT file is a device-generated activity file format commonly used by fitness watches, bike computers, and GPS devices.

In plain language, it is the kind of file that often stores a recorded outing from a watch or similar device, including movement and sensor data collected during the activity.

What FIT stands for

FIT stands for Flexible and Interoperable Data Transfer.

It is meant to be a compact file format for activity, health, and sensor data collected by compatible devices.

Who is responsible for the FIT standard

The FIT format is maintained by Garmin.

Garmin publishes the FIT SDK and related documentation, and it is effectively the steward of the format used by many fitness and outdoor devices.

Why TRIPS uses FIT files

TRIPS uses FIT files for calibration.

That means TRIPS can look at your past recorded activities and estimate how you tend to move under real-world conditions instead of relying only on generic defaults.

Depending on the file contents, FIT data can help TRIPS learn from:

movement over distance and time
grade exposure
pace behavior
heart-rate response

Without recorded activity files, TRIPS has no personal activity history to calibrate from.

What a FIT file usually contains

A FIT file often includes:

GPS track data
timestamps
moving time
distance
elevation
heart rate, if the device recorded it

The exact contents depend on the device and the activity.

For TRIPS calibration, heart rate and terrain exposure usually make the file much more useful.

What kind of data can be found in FIT files

Depending on the device and recording setup, FIT files can contain several kinds of data:

location data such as latitude, longitude, and track points
timing data such as timestamps, elapsed time, and moving time
movement data such as speed, pace, cadence, and distance
elevation data such as altitude gain and loss
physiological data such as heart rate
device and activity metadata such as sport type, lap markers, and recording intervals

Not every FIT file contains all of those fields.

For TRIPS, the most helpful files are usually the ones that include believable movement, elevation, and heart-rate data from hiking-like activities.

FIT file versus GPX file

These files serve different jobs.

A GPX file is usually a route or track you want to plan from.

A FIT file is usually a recorded activity from something you already did.

For TRIPS:

GPX is mostly for route planning
FIT is mostly for calibration

How people usually get FIT files

Common methods include:

recording an activity on a GPS watch or outdoor device
syncing that activity to the device maker's platform
exporting the activity as a FIT file from that platform
copying the original FIT files directly from the device or from a local archive

The exact steps depend on the watch, device, or service you use, but the basic pattern is usually:

Record the activity on a compatible device.
Sync or save the activity so the file exists outside the device.
Export or collect the .fit file.
Put related FIT files into a folder for calibration ingest.

What makes a FIT file useful for TRIPS

A useful FIT file for TRIPS usually reflects real hiking or backpacking behavior that resembles the trips you want to plan.

Useful files often include:

hiking, backpacking, or mountain travel
believable movement and elevation data
heart-rate coverage if available
terrain exposure relevant to the trips you care about

Common mistakes

Watch for these:

including activities that are mostly running, cycling, or gym sessions
assuming more files always means better calibration
including unusual one-off efforts that do not represent your normal trip style
forgetting that some workflows may require re-uploading FIT files in the current browser session

What to do next

If you are deciding how to assemble a calibration folder, read:

Prepare a FIT folder for calibration
Which FIT files should I include for calibration?

If your FIT folder is ready and you want to use it, read:

Ingest FIT files for calibration