If your Mac starts feeling sluggish, the fan spins up like a jet engine, or your battery begins draining rapidly, the first step in troubleshooting is finding out exactly which application is causing the problem. In macOS, you do this using a built-in utility called Activity Monitor.
Activity Monitor is the Mac equivalent of the Windows Task Manager. It provides a real-time, detailed view of how your system’s resources — including CPU, Memory (RAM), Energy, Disk, and Network — are being consumed by every open application and background process.
How to Open Activity Monitor
Activity Monitor is located in the Utilities folder, but the fastest way to open it is using Spotlight Search.
- Press Command + Spacebar to open Spotlight.
- Type Activity Monitor and press Enter.
Alternatively, you can open the Finder, go to Applications, open the Utilities folder, and double-click Activity Monitor.
Understanding the CPU Tab
When you first open Activity Monitor, it defaults to the CPU tab. This section shows how much processing power each app is using.
- % CPU: This is the most important column. It shows the percentage of a single processor core an app is currently using. Click the “% CPU” column header to sort the list so that the most demanding apps rise to the top.
- Idle vs. User vs. System: At the very bottom of the window, you will see a graph. “System” is macOS itself, “User” represents the apps you are running, and “Idle” is your unused processing power. If the Idle percentage is consistently low, your Mac is struggling to keep up with current demands.
If an app is unresponsive and using an unusually high percentage of CPU (e.g., 90% or more while you aren’t actively doing anything in it), it may have crashed or encountered a bug. You can force it to close directly from here.
Understanding the Memory (RAM) Tab
Click the Memory tab at the top of the window to see how your RAM is being allocated.
While looking at the list of apps is helpful (web browsers with dozens of tabs open usually sit at the top), the most critical information is at the bottom of the window:
- Memory Pressure: This coloured graph is the best indicator of your Mac’s health.
- Green: Your Mac has plenty of RAM available.
- Yellow: Your Mac is starting to run out of RAM and is relying on memory compression. Things might slow down slightly.
- Red: Your Mac is entirely out of RAM and is using “Swap” memory (using your much slower hard drive as temporary RAM). This drastically slows down performance.
If you constantly see a red Memory Pressure graph, you either need to close background applications or consider buying a Mac with more RAM in the future.
Understanding the Energy Tab
If you are using a MacBook and trying to maximise your battery life, click the Energy tab.
Sort by the 12 hr Power column. This shows which applications have consumed the most battery over the last half-day. Apps like Google Chrome, heavy video editors, and games will typically dominate this list. If you notice an app you rarely use sitting high on the Energy list, you should close it to preserve your battery.
How to Force Quit an App in Activity Monitor
If you identify an application in the CPU or Memory tab that is frozen, hogging resources, or generally misbehaving, you can force it to shut down immediately.
- Click the problematic app in the list to highlight it.
- Click the Stop button (an icon of an X inside an octagon) located in the top menu bar of Activity Monitor.
- A confirmation dialog will appear. Click Quit to ask the app to close normally. If the app is completely frozen and refuses to respond, click Force Quit to instantly terminate the process.
Warning: Do not force quit processes if you do not know what they are, especially ones listed as belonging to the user “root”. Terminating critical system processes can cause macOS to crash and force a restart. Stick to quitting applications you recognise.
By learning how to read the CPU and Memory tabs in Activity Monitor, you take the guesswork out of troubleshooting, allowing you to instantly identify and resolve performance bottlenecks on your Mac.