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FIT
What is a FIT file?
The binary format sports watches record natively. Compact, and unreadable without conversion.
What FIT is
FIT is a binary format, meaningful only to a program that knows it. It is used for fitness tracking.
The extension is .fit, and the full name is Flexible and Interoperable Data Transfer. Both matter less than what the file can hold, which is what the rest of this page is about.
Where FIT came from
Garmin published it in 2008. The specification is Flexible and Interoperable Data Transfer.
Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.
The specification is published, but by its owner
It is written down and implementable, though the vendor decides what the next version looks like. In practice that is enough for the file to keep opening; it is not enough to be sure of it.
Nothing is thrown away
FIT stores its content exactly. Saving it again changes nothing, so it can be opened, edited and re-saved as often as you like without accumulating damage — which is what makes it a working format rather than a delivery one.
What it does to protect itself
FIT carries a checksum, so a damaged file is detected rather than silently mis-read.
A checksum will not repair anything. It tells you the file is wrong, which is the difference between finding out now and finding out from whoever you sent it to.
What opens FIT
Garmin Connect, Strava and GoldenCheetah read it, and so do most programs of the same kind.
If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.
Opening it in a browser
No browser reads it.
That is the single most common reason to convert it: not that the format is bad, but that the place you want to show the file cannot read it.
It is a delivery format
FIT is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.
What goes wrong with it
The recurring complaints: support outside its home ground is uneven.
None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.
The facts, in one place
| Extension | .fit |
|---|---|
| Media type | application/vnd.ant.fit |
| Published by | Garmin |
| First published | 2008 |
| Specification | Flexible and Interoperable Data Transfer |