About FITS Files
FITS Astronomical Image
FITS (Flexible Image Transport System) is the standard digital file format in astronomy for storing images, tables, and metadata from telescopes and satellites. It supports multi-dimensional arrays and extensive header metadata for scientific observation records.
Family
Raster & Vector Images
Extension
.fits
MIME Type
image/fits
Can Use As
HOW FITS
CAME TO BE.
FITS — Flexible Image Transport System — was designed in 1981 by Don Wells (NRAO), Eric Greisen (NRAO), and Ron Harten (Dwingeloo Observatory) as the standard astronomical data interchange format. The IAU formally endorsed it in 1982. A FITS file is astonishingly self-documenting: every file begins with an ASCII header listing every variable, unit, coordinate system, instrument, and observation timestamp. After the header come 2D, 3D, or N-dimensional data arrays at whatever precision the telescope captured.
Every major telescope on Earth and in orbit produces FITS. Hubble, JWST, Chandra, the Very Large Telescope, every CCD-equipped backyard astronomer — all write FITS. NASA’s public Hubble archive holds over 2 million FITS files, available for anyone to download. The format is older than TCP/IP and still the backbone of astronomy in 2026. Wells’ deliberate design choice — keep the format simple, text-headered, and forever stable — is widely cited as a triumph of scientific data stewardship.
CURIOSITIES &
TRIVIA.
Every raw image from the Hubble, James Webb, Chandra, and essentially every professional telescope is a FITS file.
FITS was ratified in 1982 and has maintained complete backward compatibility — files from 1982 open identically in 2026 software.
NASA's Mikulski Archive for Space Telescopes (MAST) holds over 2 million public Hubble FITS files free to download.
FITS headers are ASCII text with 80-character records — you can open a FITS in Notepad and read the observation's metadata directly.
The format can hold images, spectra, binary tables, and any n-dimensional array — one container for astronomy's entire data spectrum.
STRENGTHS &
LIMITATIONS.
Strengths
- Self-documenting — every file carries complete observational metadata.
- Lossless — bit-exact storage of detector readouts.
- Stable since 1981 with zero breaking changes.
- Mandatory for professional astronomy — every research publication uses it.
- Open standard endorsed by IAU.
Limitations
- Niche — used almost exclusively in astronomy.
- File sizes are large (no default compression).
- Not a display format outside specialized viewers (DS9, AstroBin).
- Consumer imaging apps don't understand FITS.
Typical Sizes & Weights
Backyard-telescope CCD shot (5 MP)
10-30 MB
Hubble WFC3 single exposure
~65 MB
JWST NIRCam full detector
~650 MB
Technical Specifications
- MIME type
- image/fits
- Extensions
- .fits, .fit, .fts
- Standard
- IAU-endorsed FITS 4.0 (latest revision)
- Header records
- 80-character ASCII cards
- Encoding
- IEEE big-endian integers and floats
CONVERT FROM
FITS
Common Use Cases
Astronomy, telescope data, satellite imagery, scientific imaging
Related Formats
Popular comparisons
FITS vs JPG
Differences, file size, and when to choose each format.
FITS vs PNG
Differences, file size, and when to choose each format.
FITS vs WEBP
Differences, file size, and when to choose each format.
FITS vs AVIF
Differences, file size, and when to choose each format.
FITS vs GIF
Differences, file size, and when to choose each format.
FITS vs BMP
Differences, file size, and when to choose each format.
Popular FITS conversions
The most-requested destinations when starting from FITS.
Frequently Asked Questions about FITS
Frequently Asked Questions
FITS (FITS Astronomical Image) is an image format used to store raster graphics — a two-dimensional grid of pixels describing a picture. It is part of the raster & vector images family and designed around a specific trade-off between file size, visual fidelity, and feature support (transparency, colour depth, compression type). Photographers, web designers, and content creators choose FITS when its particular strengths match the publishing target.
Most desktop photo viewers (Windows Photos, macOS Preview, GIMP, Photoshop, Affinity Photo) open FITS natively. On mobile, iOS Photos and Google Photos display FITS in the gallery when supported by the OS. If the format is rare or new, convert to JPG or PNG first — both are universally readable — using our FITS to JPG or FITS to PNG converter.
Upload the FITS to KaijuConverter and pick a target format (JPG, PNG, WebP, HEIC, TIFF, BMP, SVG, PDF). The conversion runs in the browser via ImageMagick and returns a download in seconds. No account or installation required; both input and output delete automatically within two hours.
It depends on the task. JPG is the smallest file size for photographs; PNG is lossless with transparency; FITS has its own niche that may favour colour depth, animation, or encoding efficiency over one or both of those. For the final web publish, test all three and measure file size plus visible quality on real content.