PSB files: the 2 GB limit, slow saves and file size
PSB is Adobe Photoshop's Large Document Format. What's the difference between a PSD and a PSB file? A PSD stops at 2 GB and at 30,000 pixels on either side. A PSB goes up to 300,000 pixels a side, has no file size limit you're likely to reach, and keeps every Photoshop feature. Past those PSD limits, a layered file has to be a PSB.
Files that big save slowly, and the usual fix for slow saves makes them bigger still. This guide covers both, including what Layersqueeze can and can't do for PSB files today.
PSD vs PSB
| PSD | PSB | TIFF | |
|---|---|---|---|
| Largest file | 2 GB | No stated limit | 4 GB, or more with the BigTIFF option |
| Largest width or height | 30,000 pixels | 300,000 pixels | Not stated |
| Keeps every Photoshop feature | Yes | Yes | Saves layers, but other apps see only the flattened image |
The limits come from Adobe's help on file formats in Photoshop and saving large documents, and the file format specification. Adobe also notes that documents wider or taller than 30,000 pixels can't use some plug-in filters, even as PSB.
Is a PSB the same as a PSD? Nearly. Adobe's file format specification says the PSB format "is identical to the Photoshop native format in many ways." The layout is the same; PSB uses bigger fields for sizes so that layers and files can pass the old limits. Fewer apps read it, though. Adobe's own warning is that "most other applications and older versions of Photoshop cannot support documents with file sizes larger than 2 GB." Lightroom Classic imports PSBs up to 65,000 pixels on the long edge and 512 megapixels, if they were saved with Maximize Compatibility on (Adobe's Lightroom Classic formats page). GIMP has opened PSB files since version 3.0 and can save them since 3.2 (GIMP 3.2 release notes).
How to convert a PSB file to PSD
Open it in Photoshop, choose File > Save As (or Save a Copy) and pick Photoshop as the format. That only works if the document fits PSD's limits: 30,000 pixels or less on each side, and a saved file under 2 GB. Photoshop judges the second by the PSD it writes, and stops with a message if that would pass 2 GB. To get under the limit you'd have to give something up, such as cropping, merging layers or dropping to 8-bit, or turn Maximize Compatibility off, which our Maximize Compatibility guide covers. Otherwise, keep it as a PSB; you lose nothing by doing so as long as your apps read it.
Why big PSBs save slowly
When Photoshop saves, it compresses every layer. 8-bit layers get a fast but weak run-length compression. 16 and 32-bit layers get zip, which packs tighter and takes longer. With Maximize Compatibility on, Photoshop also writes a flattened copy of the whole canvas in addition to the layers.
On large files that adds up. In an r/photoshop thread about slow PSB saves, the poster describes 20 minutes to open a file, 2 minutes to make an edit and another 20 to save it, on a machine where doubling the memory from 64 to 128 GB cut half an hour off save times. Another user working on 30 to 40 GB files says each save still takes about an hour. They could see only one processor thread working on the save, and they suspect the compression, since turning it off speeds saving up a lot. That's also their reason for leaving it on: "I would have a severe file storage problem if I turned file compression off."
What Disable Compression costs
Photoshop's File Handling preferences have a checkbox called "Disable Compression of PSD and PSB Files." With it ticked, Photoshop writes layers uncompressed. Adobe's performance guide, updated October 6, 2026, now suggests it for 16 and 32-bit documents to speed up saving, along with setting Maximize Compatibility to Ask or Never.
Saves get much faster. Files get much bigger. Two published examples:
| Source | Compressed | Uncompressed | Save time |
|---|---|---|---|
| Fstoppers, a retouching PSB on a laptop's internal SSD | 5.38 GB | 9.7 GB | 3 min 52 s down to 1 min 18 s |
| r/photoshop, one user's file | 6 GB | 35 GB | 5 min down to 20 s |
How much bigger depends on the content: the Fstoppers file grew by about 80%, the Reddit one nearly sixfold. Fstoppers suggests a routine: work with compression off, and when the job is delivered, turn compression back on and save each file once more to get the space back. That last save is as slow as ever, and it means opening every finished file in Photoshop again.
Shrinking finished PSBs
How do you reduce PSB file size without throwing work away? In Photoshop, the options are the ones above: save with compression on and Maximize Compatibility off. Beyond that, the remaining options all cost something, such as merging layers, cropping off-canvas pixels or dropping to 8-bit; our guide on every way to reduce PSD file size goes through them, and they apply to PSB the same way.
Layersqueeze reads and writes PSB files. It stores layers with zip compression in place of run-length compression, drops the flattened copy that Maximize Compatibility saves (Photoshop doesn't use it when it opens a layered file), and clears the hidden list of pasted documents. Every pixel stays identical, and it reads the new file back and checks every layer against the original before you download it. The zip step also works on layers saved with no compression at all, which is how Disable Compression writes them, so those files are where it has the most to do. We haven't yet measured files saved that way, so we can't tell you how much it saves on them. On ordinary files, it cut 34 public Photoshop files by 46% in total, and eight studio production files by 53%. 8-bit files shrink the most; 16-bit files mostly lose the flattened copy, because Photoshop already zips their layers.
The limit is memory. Layersqueeze runs in a browser tab, and a tab can only use so much of your computer's memory. Files over about 1 GB may not fit; the largest we've run through the same code is 762 MB. So for the 6 to 40 GB files in the threads above, it isn't the answer today, and the re-save routine in Photoshop is.
If your PSBs live in a Lightroom Classic catalog, untick "Drop the flattened copy" before dropping them on the page, since Lightroom needs it to import them.
What a smaller file doesn't change
Layersqueeze keeps a PSB a PSB, even when the smaller copy comes in under 2 GB, and that copy won't necessarily save as a PSD: Photoshop judges the 2 GB limit by the file it writes itself. The saving also only lasts until Photoshop saves the file again. Photoshop rewrites the whole file its own way on every save, with its own compression and with the flattened copy if Maximize Compatibility is on. We saw this with a 58.7 MB PSD that Layersqueeze took to 19.6 MB: after one more save in Photoshop it was back to 58.7 MB, or 36.5 MB with Maximize Compatibility off. That makes Layersqueeze a tool for files you've finished: archives, backups, cloud storage and deliveries. For files you're still working on, Photoshop's own settings decide the size.
If you're not sure what's making a file big in the first place, our guide to why PSD files get so big goes through each cause.