“Your system has run out of application memory” on Mac: what it means and what to do

What the message means

The warning reads “Your system has run out of application memory. To avoid problems with your computer, quit any applications you are not using.” It comes with a Force Quit Applications window listing what’s open. It’s macOS speaking, not a website or an app, and it isn’t a virus.

Your Mac has a fixed amount of memory (Activity Monitor calls it Physical Memory). When apps ask for more than is free, macOS first compresses memory that hasn’t been used lately, which Apple describes as compressing inactive apps to make more RAM available for active ones. Then it writes pages out to the startup disk, which Activity Monitor shows as Swap Used. Apple’s developer documentation calls this disk space the backing store and says macOS uses all of the available space on the startup disk for it, instead of a preallocated partition.

So memory only “runs out” when both run dry: the chips are full and the disk can’t take more. On a Mac with plenty of free disk space, that takes an app that keeps asking for more, or a very heavy load. On a nearly full disk it happens much sooner.

The one-minute check

1. In the warning, or in the Force Quit window (press Option-Command-Esc, or choose Force Quit from the Apple menu), quit apps you aren’t using. Save your work first where you can: Apple warns that force quitting can lose unsaved changes.
2. Open Activity Monitor: press Command-Space, type Activity Monitor and press Return.
3. Click Memory, then click the Memory column header until the biggest numbers are at the top. Choose View, All Processes so nothing is hidden.
4. Look at the Memory Pressure graph at the bottom. Apple’s meanings: green, memory is being used efficiently; yellow, the Mac may eventually need more RAM; red, it needs more RAM. Next to it, Swap Used is the startup disk space standing in for memory, and Compressed is memory squeezed to make room.
5. Open System Settings, General, Storage and look at how much space is left on the startup disk.

Memory Used close to Physical Memory is normal on its own: Apple says unused memory doesn’t necessarily mean better performance, and macOS also fills spare memory with Cached Files to make apps reopen faster. Memory Pressure and Swap Used are the numbers that tell you something is wrong.

Common causes, and what to do

One app that keeps growing

If one process at the top of the Memory tab is using far more than everything else, and its number keeps rising while you watch, it isn’t giving memory back. That’s a fault in that app (often called a memory leak), and more memory in the Mac only delays it. Browsers count here too: one tab can hold several gigabytes.

What to do: save your work in that app, then quit it. If it won’t quit, select it in Activity Monitor and click the Stop button (the X in the toolbar), then Quit, or Force Quit if Quit doesn’t work. Install its updates, and if it keeps happening, tell its developer.

More open than your memory can hold

Every app, window and tab takes memory. Video editing, virtual machines, large photo libraries and dozens of tabs together can need more than the Mac has, and then Memory Pressure sits in yellow or red and Swap Used climbs.

What to do: quit apps and close tabs you don’t need; Apple’s list for a slow Mac says the same. If Memory Pressure is red with only your normal set of apps open, the Mac needs more memory than it has. To see whether yours can take more, hold Option, choose System Information from the Apple menu and click Memory: Apple says the Upgradeable Memory entry tells you, and if that pane doesn’t appear, the memory can’t be upgraded.

The startup disk is almost full

Swap lives on the startup disk, so with only a few gigabytes free there’s nowhere for memory to go. This is the cause to suspect when the warning appears with only a couple of apps open.

What to do: free space. System Settings, General, Storage shows what’s taking it, with Apple’s recommendations. Empty the Trash, since trashed files keep their space until you do, and move large files to an external drive. See Why is my Mac storage full? for the rest.

A lot of wired memory

Apple describes Wired Memory as memory the system needs that must stay in RAM and can’t be used by other apps. If it’s a large share of Memory Used, check anything you installed recently that adds drivers or system extensions: System Settings, General, Login Items & Extensions.

Still happening

• Restart. It releases everything that has built up since the last one.
• Install macOS updates from System Settings, General, Software Update, and update the app that keeps topping the Memory list.
• Start up in safe mode once. It skips login items, and Apple says it also clears certain system caches, which can free some disk space. If the warning stops in safe mode, something that starts with your Mac is the cause.

What not to do

• Don’t buy a “memory cleaner”. macOS already manages memory, and freeing it artificially only empties the cache that makes apps reopen faster. The fix is quitting what’s using memory or freeing disk space.
• Don’t force quit processes you don’t recognize. Apple warns that force quitting a process other apps depend on can cause them problems. Quit apps you opened.
• Don’t judge by Memory Used alone. A full-looking number with green Memory Pressure is a Mac using its memory well.

Keep an eye on it from the menu bar

Activity Monitor shows memory once you open it, which is usually after the warning. Multimeter keeps the totals in the menu bar as small live meters, so you see it building up:

• Memory: Memory Used counted the way Activity Monitor counts it (app memory, wired and compressed), as a percent of your Mac’s memory. Its menu shows it in gigabytes, like “12 GB of 32 GB”. It updates every 5 seconds on power and about every 10 on battery, and turns yellow above 80% and red above 90% by default. It doesn’t show Memory Pressure or Swap Used, and a high number on its own is normal, so treat red as the cue to open Activity Monitor’s Memory tab.
• Disk space: how full the startup disk is, yellow at 85% full and red at 95%. That covers the cause Activity Monitor won’t warn you about: a disk too full for swap.
• CPU: total use across all cores. An app stuck in a loop often uses memory and CPU together.

Multimeter shows totals, not which app, so it tells you when to look rather than naming the cause. Each meter can send a notification when it goes critical, and five live meters use about 3% CPU.