The short answer
Memory pressure on a Mac is Activity Monitor's measure of how hard macOS is working to keep memory available for your apps. Green means memory is used efficiently. Yellow means macOS is compressing memory. Red means the Mac needs more memory and is swapping to disk, so apps slow down. Close or restart the apps that grew.
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What memory pressure measures
macOS uses spare memory on purpose: it keeps cached files in memory and hands that space back the moment an app needs it. So “free memory” is usually small, and that's fine. Memory pressure looks at the work macOS has to do to make room: how much it is compressing, and how much it is writing to swap on the SSD.
- Green. Memory is being used efficiently. Nothing to do.
- Yellow. macOS is compressing memory to fit everything in. The Mac may still feel fine, but it is close to swapping.
- Red. The Mac needs more memory than it has. macOS is swapping, and apps wait while memory is read back from the SSD.
How to check it
Open Activity Monitor (in Applications → Utilities) and click the Memory tab. The Memory Pressure graph is at the bottom, next to Physical Memory, Memory Used, Cached Files and Swap Used. The graph's colour is the reading; its history shows whether pressure is a spike or has been high for a while.
Under the graph, Memory Used is split into App Memory, the part your apps use and the part you can change, Wired Memory, which macOS keeps in RAM for itself, and Compressed. Low free memory on its own is normal; pressure and swap are what to watch.
memory_pressure | tail -1sysctl vm.swapusagememory_pressure ends with the system-wide free memory percentage. sysctl vm.swapusage shows total, used and free swap. Swap that keeps growing while you work is the clearest sign of a real memory shortage.
What pushes pressure up
- Browsers with many tabs. Each tab and extension runs in its own helper process, and the helpers add up.
- Virtual machines and containers. Docker, OrbStack and VMs reserve memory up front.
- iOS simulators and Xcode builds. Several booted simulators can take several gigabytes each.
- An app that keeps growing. A memory leak shows up as one app's memory rising steadily over hours.
In Activity Monitor, sort the Memory tab by the Memory column. Chrome, Slack and other Electron apps appear as many rows; add up their helpers to see the real total.
What to do about it
- Quit or restart the app that grew most. For a browser, close tabs you don't need or restart it.
- Stop virtual machines, containers and simulators you aren't using.
- If pressure is yellow or red every day with your normal apps, the Mac needs more memory for your workload. Apple's guide says the same.