Guide
Mac memory pressure explained: what the green, yellow and red graph means
The first thing most people look at in Activity Monitor's Memory tab is "Memory Used", and it is almost always alarming: 14 GB of 16 GB, 7.5 GB of 8 GB. It is also almost always meaningless. macOS deliberately uses every byte it can for caching and hands it back the instant an app needs it. The number that tells you whether you have enough RAM is the memory pressure graph, and this guide explains how to read it.
Where to find it
Open Activity Monitor (Applications → Utilities), click the Memory tab, and look at the bottom. The small graph labelled Memory Pressure is coloured green, yellow or red. In Terminal, memory_pressure prints the same information as text, including the percentage of memory that is free.
What the colours mean
| Colour | What macOS is doing | What you should do |
|---|---|---|
| Green | Serving every request from RAM. Any compression or swapping is trivial. | Nothing. The used figure is irrelevant while the graph is green. |
| Yellow | Compressing memory and beginning to swap to the SSD to make room. | Close apps or tabs you are not using. If it is yellow most of the day, you are running more than this Mac's RAM is comfortable with. |
| Red | Swapping heavily. Apps stall while their memory is read back from the SSD. | Quit something now. If this happens regularly, you need more RAM for your workload or a lighter set of apps. |
The important point: pressure measures how hard macOS is working to satisfy memory requests, not how much is in use. A Mac with 15.5 GB of 16 GB used and a green graph has no memory problem at all.
The five numbers under the graph
- App Memory: memory your apps have actually asked for. The one figure that goes down when you quit things.
- Wired Memory: used by the kernel and drivers. Cannot be compressed or swapped. Grows with the number of displays, GPU work and open files.
- Compressed: inactive memory squeezed to make room instead of swapping. A few gigabytes compressed is normal and fast to decompress.
- Cached Files: recently used files kept in RAM so they open instantly. This is the part that makes "Memory Used" look scary; it is free for the taking.
- Swap Used: memory that has been written to the SSD. A few hundred megabytes after days of uptime is nothing. Several gigabytes, plus yellow or red pressure, is the real sign of a RAM shortage.
Unified memory on Apple Silicon
On M-series Macs the CPU and GPU share one pool of memory. That makes graphics work fast, and it also means a game, a video editor or a large external display at a scaled resolution eats into the same RAM your apps use. It is why an 8 GB Mac feels fine for writing and browsing and runs out of room the moment you add Lightroom and a 4K monitor. The pressure graph tells you when you have crossed that line.
Does swapping wear out the SSD?
Every write to the SSD uses a little of its finite endurance, and heavy swapping writes a lot. For most people the amount is small compared with the drive's rating and nothing to worry about. If your Mac spends its days in yellow or red, the swap traffic is one more reason to fix the underlying shortage rather than live with it.
How to bring pressure down
- In Activity Monitor's Memory tab, sort by the Memory column. Browsers, Electron apps (Slack, Discord, Notion, VS Code) and virtual machines are the usual leaders.
- Close tabs rather than windows; each tab is a process.
- Restart apps that have been open for days. Memory that leaks slowly looks like a gradually rising App Memory figure.
- Use an external display at its native or default resolution; scaled resolutions cost wired memory as well as GPU power.
- Reboot occasionally. It is unglamorous and it works.
Watching it without Activity Monitor
A menu bar monitor shows memory pressure and the breakdown at a glance. Stats and iStat Menus both do this well. Our own ThermPort shows memory used in the menu bar and, one click away, the pressure state, the app / wired / compressed split, swap, and the top five processes by memory, so the "what is eating my RAM" question has a one-second answer.
Frequently asked questions
Is it bad if my Mac shows 90% memory used?
Not by itself. macOS fills unused memory with cached files on purpose and gives it back instantly when an app needs it. Look at the memory pressure graph instead: green means the Mac is fine, whatever the used figure says.
What does 'Swap Used' mean on a Mac?
Memory that macOS has moved to the SSD because RAM ran out. A few hundred megabytes is normal after days of uptime. Several gigabytes, together with yellow or red pressure, means you are short of RAM for what you run.
Is yellow memory pressure a problem?
It is a warning, not a failure. macOS is compressing memory and starting to swap, and you may notice slowdowns when switching apps. Close what you are not using; if it is yellow all day, more RAM would help.
Will more RAM make my Mac faster?
Only if memory pressure is regularly yellow or red. A Mac that stays green is not limited by RAM, and adding more would change nothing you can feel.
ThermPort puts CPU temperature, fan speed, memory, power and more in your Mac's menu bar in a 15 MB app. 14-day free trial, one-time purchase, Apple Silicon only.
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