Find the process using the most CPU on Mac

The fans on a MacBook only really fire up when something is eating real CPU, and the something is usually a single rogue process you didn’t realise was running. Finding it is fast — the trick is knowing which tool gives you the answer in fewest clicks.

The fastest paths

Activity Monitor

The default, and perfectly good.

1. Launch Activity Monitor.
2. Click the CPU tab.
3. Click the %CPU column header to sort descending.
4. The top row is your culprit. Sustained > 50% on a single process is usually worth investigating.

A small note — macOS reports CPU as a percentage of one core, so a process at 400% is using four full cores. That’s normal for video encodes, builds, ML inference. Not normal for “Word.”

Terminal: top

The fastest read if you have a terminal open already:

top -o cpu -stats pid,command,cpu,mem -n 10

That sorts by CPU, trims to ten rows, and shows the columns you actually care about. Press q to quit. Add -l 1 if you just want a single snapshot instead of a live updating view.

For a richer ncurses interface, brew install htop and run htop — colour-coded bars, tree view, click-to-kill.

Menu bar monitor

If you’d rather not launch anything, a menu-bar CPU readout makes the question answerable with one glance. Beacon’s CPU display sits in the bar and the click-through panel lists the top CPU processes.

1. Install Beacon and add CPU to your menu bar in Settings > Menu Bar.
2. When the number spikes, click it — top three CPU users appear, with their percentages.
3. Click any process to open Activity Monitor on that PID.

Reading what you find

Some common patterns:

• kernel_task at high CPU — usually thermal management. Cool the Mac (vents, surface, fan curve) rather than killing the process; you can’t kill it anyway.
• WindowServer at 50%+ — graphics-heavy app, external monitor, or a stuck animation. Quitting recent apps usually fixes it.
• mds / mds_stores / mdworker_shared — Spotlight indexing. Let it finish (usually 5-30 minutes after a big file change).
• backupd — Time Machine. Same advice; let it finish, or pause it temporarily.
• A browser renderer at hundreds of percent — bad tab. Close tabs until the number drops, then reopen one at a time.
• An Electron app doing the same — usually a stuck websocket or bad extension; restarting the app fixes it 95% of the time.

The key habit is checking quickly enough that you catch it while it’s happening. The longer a runaway runs, the more battery, heat, and lifespan it costs your machine.