What Is an ARW File? Sony's RAW Format, Explained
An ARW file — short for Alpha RAW — is the RAW photo format written by Sony Alpha cameras. It is not a finished image. It is the unprocessed data from every photosite on the sensor at the moment you pressed the shutter, plus the camera's metadata and a JPEG preview, packed into one .ARW file. Think of it as the digital negative: everything the camera saw, before anyone decided what the photograph should look like.
That one distinction — data, not image — explains almost everything people find confusing about ARW files: why they need special software, why they look flat next to the camera's JPEG, and why they're two to three times the size. Here's the rest. Short on time? See how to open ARW files on a Mac or how to convert ARW to JPEG.
ARW at a glance
| Full name | Sony Alpha RAW |
|---|---|
| Extension | .ARW |
| What it holds | Unprocessed sensor data, EXIF metadata, embedded JPEG preview |
| Structure | Based on TIFF, like most camera RAW formats |
| Bit depth | Typically 14-bit (16,384 tonal levels per channel, against a JPEG's 256) |
| Typical size | About 14–130 MB depending on megapixels, compression setting and scene detail |
| Opens with | macOS Preview and Photos, Sony Imaging Edge, and RAW editors such as RevelRaw, Lightroom or Capture One |
What's actually inside an ARW file
A camera sensor doesn't record a picture. Each photosite records how much light hit it through a single-color filter — red, green or blue — arranged in a mosaic. An ARW file stores those readings as they came off the sensor:
- The mosaic sensor data. One brightness value per photosite, at 14-bit precision. No white balance, no sharpening, no color profile has been applied yet. Turning this mosaic into a viewable photograph — called demosaicing — is the job of your RAW editor.
- Metadata. Camera body, lens, exposure settings, focus points, and the picture profile you had dialed in. Editors read this to know how to interpret the data; nothing in it is baked into the pixels.
- An embedded JPEG preview. The camera develops a small JPEG with its own processing and tucks it inside the ARW. This is what you see on the camera's screen and in Finder thumbnails — which is why a RAW file can look one way as a thumbnail and another once an editor opens the real data.
Why an ARW looks flat next to the camera's JPEG
When you shoot JPEG, the camera develops the photo for you: it picks a white balance, boosts contrast and saturation, sharpens, and throws away the data it no longer needs. When you shoot RAW, all of those decisions are still yours to make. So when an editor first opens the ARW with neutral settings, you're seeing the undeveloped negative — flatter, softer and duller than the confident JPEG the camera showed you. That's not lost quality. It's headroom: the highlight detail, shadow depth and color latitude the JPEG would have discarded are all still in the file, waiting for your version of the photograph. Our RAW vs JPEG guide shows exactly what that headroom rescues.
How big is an ARW file? Real sizes from our a7 V
It depends on the body and on the RAW file type you pick in the camera's menu. Rather than quote spec-sheet estimates, we measured our own: the ARW files we shot on our own a7 V, a 33-megapixel body, from June to September 2026, with each size read from the file's metadata.
| RAW file type | Files measured | Median size | Range |
|---|---|---|---|
| Compressed | 532 | 26.2 MB | 14.0–35.2 MB |
| Lossless Compressed | 14 | 44.1 MB | 41.7–45.4 MB |
Lossless Compressed keeps every bit the sensor recorded, shrunk like a ZIP; Compressed discards a little data in ways you'll almost never see. On our files, lossless came out about 1.7 times the size of a typical compressed frame. For planning, that means a 128 GB card holds roughly 4,900 compressed files or 2,900 lossless ones, and every thousand compressed frames adds about 26 GB to your drive.
Why does a compressed file swing from 14 to 35 MB? The compression spends fewer bits where the scene is smooth and more where it is busy. A clear sky or a plain wall squeezes down; foliage, gravel, fabric and high-ISO noise don't. So a day of detailed landscapes fills a card faster than a day of studio portraits against seamless paper.
There is no uncompressed row because the a7 V doesn't offer it: its RAW File Type menu lists Lossless Comp, Compressed (HQ) and Compressed. Bodies that do, such as the a7 IV, write uncompressed files about twice the size of their compressed ones, and a 61-megapixel a7R V writes uncompressed files over 120 MB. A JPEG of the same scene is a fraction of any of these, because it keeps only one finished interpretation and throws the rest away.
One more thing: ARW isn't frozen
Sony has revised the format across camera generations, which is why software sometimes lags the cameras. When a new Alpha body ships, Apple has to add its files to macOS before Preview and Photos will open them, and every RAW editor has to update its own support. If your brand-new camera's files won't open, the file isn't broken — your software just hasn't met that body yet. The fixes are in our guide to opening ARW files on a Mac. The RAW file types change too: the a7 V dropped Uncompressed and added Compressed (HQ), and our test of every Sony RAW compression mode shows what each one keeps.
How to open and convert ARW files
On a Mac you already have the basics: Preview and Photos open ARW files from most Sony bodies, and can export them to JPEG when something refuses the RAW — the full walkthrough is in our ARW to JPEG guide. To actually develop the file rather than just view it, you need a RAW editor. RevelRaw is ours: a native macOS editor for every major camera brand, with its own ARW pipeline, AI scene detection that ranks 50+ presets against your photo, and the standard fine-tune controls. Everything runs on your Mac; no file ever leaves it.
Should you keep your ARW files?
Yes, for any photograph you might care about again. The ARW is the negative; every JPEG you export from it is one interpretation, fixed forever at the settings you chose that day. Keep the ARW and you can return in five years — with better taste, better software, or a client who suddenly needs a print — and develop it again from everything the sensor recorded. Storage is cheaper than a reshoot.
FAQ
What does ARW stand for?
Alpha RAW — Sony's RAW format, named for its Alpha camera line. Every Alpha body set to shoot RAW writes .ARW files.
Is an ARW file better than a JPEG?
It holds far more data — 14-bit tonal depth against JPEG's 8, with nothing baked in — so it survives editing a JPEG can't. But it isn't a finished image and needs software to develop it. If you need files that are done straight out of the camera, JPEG is the honest choice.
How do I open an ARW file?
On a Mac, double-click it: Preview handles files from most Sony bodies. Files from a just-released camera may need to wait for a macOS update. RevelRaw has a second decoder built in, so new cameras often work in RevelRaw first. It opens 99.5% of the files in the PIXLS.US public RAW archive. On Windows, Sony's free Imaging Edge reads them.
Why are ARW files so big?
They store what every photosite on the sensor recorded, at 14-bit depth. On our own 33-megapixel a7 V, compressed files came to a median of 26 MB and lossless compressed files 44 MB. Bodies that offer uncompressed RAW write files about twice the size of their compressed ones.
Can I delete ARW files after converting to JPEG?
You can, but the JPEG holds only one interpretation of the shot. Delete the ARW and you can never re-edit with more latitude than that JPEG allows. Keep the negatives.
Related reading: Sony RAW editing on a Mac · How to open ARW files on a Mac · How to convert ARW to JPEG · RAW vs JPEG on a Sony Alpha · All RAW formats RevelRaw opens