Memory Pressure on a Mac: What Yellow and Red Mean
Used memory on a Mac is almost always high, and that's fine. How to read the Memory Pressure graph, swap and compressed memory, and when RAM really runs short.
Don’t look at Memory Used — look at the Memory Pressure graph on the Memory tab of Activity Monitor. Green means memory is fine, yellow means the Mac may need more over time, red means it’s running short and it’s time to close something heavy.
“Memory Used: 15 GB of 16.” It looks as if the Mac is about to choke. In reality that number tells you very little: a Mac showing it can run perfectly well or crawl, and only the pressure graph tells the two apart.
Why memory is always full
Free memory is wasted memory. macOS keeps it busy with cache: recently opened files, pieces of apps you’ve quit, data you might need again. When something more important asks for memory, the cache steps aside immediately.
Say you open Safari and Xcode, work for a while and quit both. Memory used doesn’t drop back to where it was, and that’s correct. Open Xcode again half an hour later and it launches faster. That’s why the slow Mac diagnosis checks memory by the graph, not by the number.
Where to look
Open Activity Monitor (Applications → Utilities) and switch to the Memory tab. At the bottom of the window are a graph and a column of numbers:
- Memory Pressure — the graph this whole guide is about;
- Physical Memory — how much RAM is installed;
- Memory Used — how much is in use right now. Next to it is the breakdown: App Memory, Wired Memory (what the system itself needs; it always stays in RAM) and Compressed;
- Cached Files — cache held in otherwise unused memory, which the system hands back on demand;
- Swap Used — how much data has been moved out to the disk.
Three colors
Apple’s guide explains the graph’s colors this way: green means your Mac is using its RAM efficiently; yellow means it might eventually need more; red means it needs more.
In practice:
- green — all good, no matter how much is “used”;
- yellow — macOS is compressing noticeably and may be writing to disk; you may notice short stalls when switching apps;
- red — the Mac is visibly slow; time to close something.
“Green graph and three gigabytes of swap” is perfectly normal. Worry about the color, not the number.
The graph runs over time, so read the stretch of the last few minutes, not a single point. A brief yellow spike when you open a heavy project is routine: macOS compressed what it could and settled down. A long yellow band that won’t drop while you work is the cue to find out what’s taking the memory.
Compression and swap
When memory starts running short, macOS first compresses data that hasn’t been used recently, right there in RAM — that’s the Compressed line. The technique arrived back in OS X Mavericks. Compressing and decompressing is faster than writing to disk. A few gigabytes in Compressed is nothing to worry about: it means macOS saved space without touching the disk.
If that’s not enough, compressed data goes to swap files on the startup
disk, in /System/Volumes/VM. The SSD in a Mac is fast, but still slower
than RAM, so heavy swapping is noticeable.
Swap on its own isn’t a disease. The warning sign is swap that keeps growing hour after hour while the graph stays yellow. How much swap is normal, how to tell whether it’s growing and whether it wears out the SSD is covered in the swap guide.
What ate the memory
On the same tab, click the Memory column header to bring the hungriest processes to the top. Usual suspects:
- a browser with dozens of tabs — each tab often runs as its own process;
- an app that has been running for days and slowly leaks, taking more and more without giving anything back;
- virtual machines and containers, which often reserve memory up front.
What to do: quit what you don’t need or restart the culprit. There’s no point “cleaning” memory with special apps — a minute later it’s full of cache again.
When you really are short on RAM
One yellow evening while exporting video is no reason to buy a new Mac. A graph that’s yellow or red on ordinary work for a week straight, though, is data. How to run that week-long check is covered in is 8 or 16 GB enough.
Checking from Terminal
For the curious, two commands:
memory_pressurewith no arguments prints statistics on memory pages, compression and swap, and ends with the system-wide free memory percentage. Run it without arguments: with-lor-pit creates memory pressure itself;sysctl vm.swapusageprints one line: how much swap space is allocated, used and free.
In the app
Mac Resources has a small Memory widget: it shows memory used the same way Activity Monitor does, draws a graph for the past hour and labels the amount like “24 of 128 GB”. The medium Resources widget shows rings for CPU, memory, disk and battery. Widgets refresh once a minute.
The menu bar item shows whichever of CPU, memory or GPU is busiest, updates every two seconds and turns red above 80%. If it’s showing memory, memory is what’s working hardest right now.
To be clear: the app doesn’t show memory pressure or swap separately, and it has no process list. For the graph’s color and the culprit, go to Activity Monitor.
If the slowdown doesn’t look like a memory problem, walk through the step-by-step diagnosis, and for more on the tool itself see the Activity Monitor guide.