What Is a PSB File?

If you already know what a PSD file is, you know most of the answer. Adobe’s file format specification describes PSB as identical to the Photoshop format in many ways; the difference is scale.

So "what is a PSB file?" comes down to one thing: a PSD that needed bigger limits. Everything else, including why fewer apps open one, follows from that.

PSB is the extension of Photoshop’s Large Document Format, made for artwork that outgrows PSD. It differs from PSD in four ways:

• Up to 300,000 px per side

  A PSD stops at 30,000 pixels in width or height. A PSB file allows 300,000 pixels in either direction, per Adobe’s specification.

• No 2 GB ceiling

  A PSD file cannot pass 2 GB. A PSB has no practical size limit, so a document with dozens of full-size layers can keep growing.

• Every Photoshop feature

  Adobe states that all Photoshop features, such as layers, effects and filters, are supported in PSB. Nothing is flattened or dropped because of the format.

• Same layout, wider fields

  Inside, a .psb file is laid out like a PSD, but its header has a different version number and its length fields are wider, to record sizes past 2 GB. Reading PSD does not mean reading PSB.

Photoshop never switches to PSB by itself. You choose Large Document Format (*.PSB) in File > Save As. Adobe’s help page recommends it for images larger than 30,000 pixels in width or height, or for documents over 2 GB. In practice, a PSB file turns up in a few situations:

• Large-format print — billboards, trade-show walls, banners and wallpaper, where the pixel size at print resolution passes 30,000 on the long side.
• Panoramas and stitched scans — very wide panoramas, maps and artwork scanned in tiles and merged into one document.
• Heavy layer stacks — retouching files, matte paintings and composites with many full-resolution layers or smart objects. These can pass 2 GB even at a normal canvas size.
• A PSD that will not save — Photoshop refuses to save a PSD past the 2 GB limit and reports that the document exceeds it. Saving the same document as PSB is the fix.

One caveat from Adobe: even in a PSB, some plug-ins may not work once a document passes 30,000 pixels on a side. The format has room for huge files; not every tool around it does.

Opening a PSB file depends on two things: whether the app reads the format, and whether your computer has the memory for it. We checked each option against its developer’s own documentation in October 2026.

• Images2Layers PSD viewer

  Free · in your browser

  Our PSD viewer reads PSB as well. Drop a .psb file onto the page and it opens in your browser tab: the full image, every layer with its name, visibility switches and PNG export. The file is read on your device and nothing is uploaded.

  Keeps

  • Layer names, order and visibility
  • Works on any computer with a modern browser
  • Your file never leaves your device

  Loses

  • Files over 300 MB or 100 megapixels
  • 32-bit, CMYK and Lab documents
  • Editing: it is a viewer, not an editor

• Adobe Photoshop

  Paid · the native app

  The format’s home. Photoshop opens a PSB with File > Open and keeps everything: layers, masks, smart objects, live text and effects. It is the reference for how the file is meant to look.

  Keeps

  • Every layer, mask and effect
  • Live, editable text
  • Saves back to PSB or, if the document fits, PSD

  Loses

  • Needs a paid subscription
  • Huge files need plenty of RAM and scratch disk
  • Some plug-ins fail past 30,000 px

• Photopea

  Free · in your browser

  The browser-based editor lists .psb among the file types it opens, next to PSD. It works inside your browser’s memory, so a PSB that is very large once decompressed can fail to load, especially on a phone or a laptop with little RAM.

  Keeps

  • Layers you can edit, not only view
  • Nothing to install
  • Saves PSD; exports PNG, JPG and PDF

  Loses

  • Large files can exhaust browser memory
  • Complex effects may not match Photoshop exactly

• GIMP 3

  Free · desktop

  GIMP has imported PSB files since version 3.0, and GIMP 3.2 added PSB export. Older 2.10 installs cannot open them, so update before you try.

  Keeps

  • Free and works offline
  • The layer stack and masks
  • Can save back to PSB from version 3.2

  Loses

  • Live text may not stay editable
  • Not every adjustment or effect carries over

Renaming the file will not help: changing .psb to .psd does not convert anything, because the inside is laid out differently. Use a converter or Save As in an editor instead. Our guide to opening a PSD file compares the same apps for ordinary PSDs.

Most people with a .psb file want something they can send or print. Our free converters read PSB as well as PSD and run entirely in your browser, so nothing is uploaded.

1. 1
   PSB to JPG — For a flat picture to share, use PSD to JPG. Pick the quality and a background colour for transparent areas, and convert a whole batch at once.
2. 2
   PSB to PNG — To keep transparency, or to get every layer as its own image, use PSD to PNG.
3. 3
   PSB to PDF — For a review copy or a print proof, PSD to PDF puts the image on a page, and can add one page per layer.
4. 4
   PSB to PSD — Only possible when the document fits inside the PSD limits of 30,000 px per side and 2 GB. Open it in Photoshop, shrink the canvas or merge layers if needed, then Save As Photoshop (*.PSD). Photopea and GIMP 3 can also save a PSD.

Converting to JPG, PNG or PDF is one-way. The result is a flat copy, and the layers stay in the original PSB file, so keep it.

All three can hold large, layered Photoshop artwork. They differ in how big they can get and in who can read them:

The rule of thumb: save as PSD while you can, switch to PSB when Photoshop makes you, and export a TIFF, JPG or PDF for anyone who only needs the finished picture. The PSD file type guide goes deeper into how PSD compares with TIFF and PNG.

A PSB file is usually big for a reason, and a browser tab has hard walls that a desktop app with a scratch disk does not. Here is what applies to our viewer and converters:

• Memory — Every layer is decoded to raw pixels at four bytes per pixel. One 20,000 × 20,000 px layer alone needs about 1.6 GB, more than a browser tab can usually hold.
• The 100-megapixel cap — Documents above 100 megapixels (10,000 × 10,000 px, for example) are refused with a plain message instead of crashing the tab.
• 300 MB per file — Larger files are not opened.
• Bit depth and colour mode — 8- and 16-bit RGB, grayscale, indexed and bitmap documents open; 16-bit files are shown at 8 bits. 32-bit, CMYK and Lab documents do not open yet.

So our tools handle the smaller PSB files, such as documents saved as PSB for their file size or just past the PSD limits. For the truly huge ones, use Photoshop or GIMP on a machine with plenty of RAM and export a smaller copy.