1. Activity Monitor's CPU tab
Open Activity Monitor (press ⌘ Space and type its name) and click CPU. Each row is a process; click the % CPU column to sort. The panel at the bottom shows the whole system: User (your apps), System (macOS) and Idle (unused).
2. A live CPU meter in the Dock
With Activity Monitor open, choose View › Dock Icon › Show CPU Usage. Its Dock icon becomes a small live graph, which stays visible while Activity Monitor is running.
3. Floating CPU windows
Activity Monitor's Window menu has CPU Usage (⌘ 2) and CPU History (⌘ 3): small windows with a bar per core that you can keep beside your work.
4. Terminal
Run top -o cpu for a live list sorted by CPU (press q to quit). For a one-line summary, run top -l 1 | grep "CPU usage".
5. A menu bar app
Menu bar apps keep CPU usage visible without opening anything. Some show numbers and graphs; Puff shows it as a mood instead (see below).
What the numbers mean
| You see | It means |
|---|---|
| An app above 100% | It's using more than one core. 400% is four cores flat out |
| High Idle in the bottom panel | Your Mac has plenty of capacity to spare |
kernel_task near the top | macOS is limiting the chip to cool it. Look for the app causing the heat |
| Short spikes to 100% | Normal. Launching apps and loading pages briefly uses every core |
| One app near 100% for minutes while idle | Probably stuck. Quit it and reopen |