Your system has run out of application memory: on a full disk, the fix is free space
This macOS warning is about memory, but on a nearly full disk the cause is often no room for swap. How to tell which you have, and what to do next.
A window pops up: Your system has run out of application memory, with a list of apps to force quit. It sounds like you need more RAM. Sometimes you do. But on a Mac that is also low on disk space, the actual shortage is often the disk.
Why a full disk causes a memory warning
When apps need more memory than the Mac has, macOS moves some of it to the disk in swap files. That is normal and happens on every Mac. If the disk is nearly full, there is no room for swap to grow, so macOS runs out of somewhere to put memory and shows this warning.
# How much swap is in use
sysctl vm.swapusage
# How much disk is free
df -h /System/Volumes/DataWhich one is it?
| You see | Likely cause | Fix |
|---|---|---|
| Under 5 to 10 GB free on disk | No room for swap | Free disk space first |
| Plenty free, swap very large | An app using far too much memory | Quit that app |
| Plenty free, warning with normal use | More work than the Mac's memory | Fewer apps and tabs at once |
What to do right now
- Save your work in open apps.
- Force quit the app at the top of the list, often a browser with many tabs.
- Free a few GB of disk: empty the Trash, delete a large download. Startup disk almost full has fast options.
- Restart. This clears swap files and gives memory a fresh start.
Check what was using memory
Open Activity Monitor, click the Memory tab and sort by Memory. The graph at the bottom shows Memory Pressure: green is fine, yellow is busy, red is struggling.
Swap files and the sleep image are covered in sleepimage and swap.
Common questions
What does your system has run out of application memory mean?
macOS cannot find room for apps' memory, either in RAM or in swap files on the disk. On a nearly full disk, swap cannot grow, which triggers it.
Can low disk space cause a memory error on a Mac?
Yes. macOS uses disk space as extra memory through swap files. With very little free space, it runs out of room and shows the memory warning.
How much free space does a Mac need to avoid memory warnings?
Keep at least 10 to 20 GB free, more if you use many apps at once. That leaves room for swap to grow.