If your Mac’s cooling fans are spinning loudly, or your entire system feels sluggish and unresponsive, the fastest way to diagnose the problem is by using Activity Monitor. This built-in utility is the macOS equivalent to the Windows Task Manager. It shows you exactly which applications are hogging your processor (CPU) or eating up your memory (RAM).
How to Open Activity Monitor
The fastest way to open the app is using Spotlight Search:
- Press Command (⌘) + Space bar.
- Type Activity Monitor.
- Press Enter.
(You can also find it by opening Finder, navigating to Applications, opening the Utilities folder, and double-clicking the app).
How to Check CPU Usage
When the app opens, click the CPU tab at the top of the window.
- Sort by usage: Click the column header labeled % CPU until the small arrow points downwards. This sorts all your running apps so the ones using the most processing power are at the top of the list.
- Analyze: It is normal for heavy apps (like video editors or complex web apps) to use a high percentage. However, if a background process you do not recognize is stuck at 99%, it might be frozen or malfunctioning.
How to Check RAM (Memory) Usage
Click the Memory tab at the top of the window.
- Sort by usage: Click the Memory column header to see which apps are consuming the most RAM. Web browsers with dozens of tabs open are usually the biggest culprits.
- Memory Pressure Graph: Look at the bottom of the window. You will see a box labeled “Memory Pressure” with a colored graph.
- Green: Your Mac has plenty of RAM available.
- Yellow: Your Mac is starting to run out of memory.
- Red: Your Mac is completely out of RAM and is relying on your hard drive to function, which severely slows down the system. You need to close some apps.
How to Force Quit an Unresponsive App
If you find an app that is completely frozen (Activity Monitor often highlights these with red text saying “Not Responding”), you can kill the process directly from this window.
- Click on the frozen app’s name in the list to highlight it.
- Click the Stop (X) icon located in the top-left toolbar of the Activity Monitor window.
- A confirmation box will appear. Click Force Quit to instantly terminate the app. Note: You will lose any unsaved work in that specific application.