How to Check CPU Usage on a Mac: Activity Monitor Guide

There’s no Task Manager on a Mac — Activity Monitor does the job. Open it (⌘-Space, type “activity”, Return) and go to the CPU tab: the % CPU column shows how much each app takes.

The bottom of the CPU tab shows how much of the processor is busy and how much is idle. The other tabs do the same for memory, battery, disk and network, and Activity Monitor can quit an app that has locked up. It looks austere, but it is simple once you know where to look.

One tab, one question: who is using the CPU, memory, battery, disk or network. Everything else is detail.

How to open it

• Spotlight: press ⌘-Space, type “activity” and press Return;
• Finder: Applications → Utilities → Activity Monitor;
• Dock: while it is running, Control-click its icon and choose Options → Keep in Dock so it is always one click away.

If a single app has frozen, you don’t even need Activity Monitor. Press ⌥⌘Esc to open the Force Quit window, the closest thing to Ctrl+Alt+Del. Select the app and click Force Quit.

What every tab has in common

The top half lists processes; the bottom half summarises the tab. The same tricks work everywhere:

• click a column heading to sort, click it again to reverse the order;
• the search field in the top-right corner finds a process by name;
• the View menu picks what to list: All Processes, My Processes, System Processes, Windowed Processes and more; View → Columns adds columns;
• double-click a process to open a window with its details;
• the ⓧ button in the top-left corner quits the selected process. Quit is the polite option, the same as ⌘Q inside the app. Force Quit is immediate, and anything unsaved is lost.

Leave system processes and other users’ processes alone: if other apps rely on a process, they can misbehave once it is gone, and quitting someone else’s process takes an administrator password. When in doubt, don’t quit it — restart the Mac instead.

CPU

The % CPU column is the share of the processor a process is using. Don’t panic at 180% or 350%: the figure is counted per core and added up, so on a multi-core Mac one process can go well past 100%. The bottom of the window shows System, User and Idle: how much macOS takes, how much your apps take, and how much is sitting unused. The overall CPU usage percentage is System plus User; the CPU LOAD graph next to them shows how it has changed. It also shows the total number of processes and threads.

In Terminal, top -o cpu gives the same: a CPU usage line at the top with user, sys and idle percentages, then processes sorted by CPU usage; press q to quit.

Say the fan is roaring and the laptop is warm. Sort by % CPU and the culprit rises to the top — often something like a browser tab running a heavy site. A process that has stopped responding is marked Not Responding and shown in red. Close the tab or quit the app normally first; force quit only if that fails.

Memory

The Memory column shows how much each process takes, but the real signal is at the bottom: the Memory Pressure graph. Green means memory is fine. Yellow means the Mac may need more. Red means it is running short. Next to it, Swap Used tells you how much macOS has pushed out to disk. How much swap is normal is covered in the swap guide.

Memory Used nearly always looks high, and that is not a problem: macOS fills spare memory with cached files. Watch the colour of the graph instead. There is more in the guide to memory pressure, and if you are shopping for a new Mac, in 8 GB or 16 GB?.

Energy

• Energy Impact — a relative measure of how much power an app is using right now; lower is better;
• 12 hr Power — the same, averaged over the last twelve hours; this column only appears on laptops;
• Preventing Sleep — whether the app is keeping the Mac awake.

If your MacBook drained itself in your bag, look for “Yes” in that column. Terminal gives more detail: pmset -g assertions lists who is holding the Mac awake and why. To keep it awake yourself when you need to, see how to keep your Mac awake. Desktop Macs have no battery summary at the bottom.

Disk

This tab shows how much each process has read and written, in the Bytes Read and Bytes Written columns. Big numbers are normal after a macOS update, while Spotlight is indexing, and during a Time Machine backup. It is worth a look when an app you aren’t using keeps writing heavily.

Network

Sent Bytes and Rcvd Bytes, per process. Sort by Rcvd Bytes to find what is downloading. The bottom shows the totals and a graph you can switch between Packets and Data.

In Terminal, nettop -P shows live traffic per process; press q to quit. More on traffic in how to see who is downloading.

Small things worth knowing

• View → Dock Icon turns the Dock icon into a live graph: CPU usage, CPU history, disk activity or network usage;
• Window → CPU Usage and Window → CPU History open small windows with a per-core graph;
• View → Update Frequency — by default the data refreshes every five seconds. Very often (1 sec) is more precise, but Activity Monitor itself then uses more CPU;
• Load always in view — rather than keeping Activity Monitor open, add a menu bar monitor or a desktop widget.

Scary-looking processes you will meet

• kernel_task — the macOS kernel. One of its jobs is to cool the CPU by taking time away from whatever is overloading it. A high number here is a symptom of heat, not its cause: look for what was heating things up. More in the kernel_task guide.
• WindowServer — composes your windows into what you see on screen and routes input events. It grows with lots of windows, external displays and animation — see the WindowServer guide.
• mds, mds_stores, mdworker — Spotlight indexing your files. They can stay busy for a while after an update or after copying big folders, then settle down.
• backupd — Time Machine making a backup.

These are part of the system; there is no need to quit them.

In the app

Activity Monitor is for investigating once things are already slow. Mac Resources is a constant gauge that lets you notice load earlier. Its menu bar badge shows an icon and the percentage of whichever of CPU, memory and GPU is busiest. It refreshes every two seconds, turns red above 80%, and you can move it with ⌘-drag. The CPU and Network widgets draw an hour-long graph, and Last Hour shows every metric at once, so you can see when the trouble started.

To be clear: Mac Resources does not show processes, temperatures or fans — the macOS sandbox doesn’t give access to them. For the culprit, come back to Activity Monitor. The app reads only load counters, collects no data, and goes online once every six hours to check for a new version. If you turn on Prevent Sleep in the badge menu, pmset -g assertions shows it as “Resources Mac: keep awake”.

If your Mac is already slow and you don’t know where to start, walk through the step-by-step diagnosis.