% CPU

Activity Monitor adds up the time a process spends on every core. If an app runs work on three cores at full speed, it shows about 300%. That is normal for apps built to use many threads, such as video editors, compilers, and browsers.

The System, User, and Idle figures at the bottom of the CPU tab work differently. They describe the whole processor, so together they add up to 100%.

% CPU measures how much of the time a core is busy, not how fast that core is running. On Apple silicon, performance cores and efficiency cores can both show 100% while doing very different amounts of work.

It also does not show whether an app is responsive. An app can be frozen at 0% CPU while it waits on something, or stay responsive at 400%.

Open Activity Monitor, click the CPU tab, and click the % CPU column header to sort from highest to lowest. Watch for a few seconds, since values change with each update.

In Terminal, top -o cpu shows the same list sorted by CPU use. Press q to exit.

The ceiling for % CPU is 100% times the number of cores macOS can schedule work on. You can look that number up in Terminal instead of guessing.

1. Open Terminal from Applications > Utilities.
2. Run sysctl -n hw.logicalcpu. This prints the number of logical cores.
3. Multiply that number by 100. That is the most % CPU all processes together can show, and the most a single process can reach if it keeps every core busy.
4. On a Mac with Apple silicon, run sysctl hw.perflevel0.logicalcpu hw.perflevel1.logicalcpu to see how many of those cores are performance cores and how many are efficiency cores.

On an Intel Mac with Hyper-Threading, each physical core appears as two logical cores. sysctl -n hw.physicalcpu shows the physical count and sysctl -n hw.logicalcpu shows the logical count, and % CPU is measured against the logical count. So an Intel Mac with four physical cores can show a process at up to 800%.

Apple silicon does not use Hyper-Threading, so the physical and logical counts are the same. The difference on Apple silicon is the mix of performance and efficiency cores. A process at 100% on an efficiency core gets less work done than one at 100% on a performance core.

If you want to know whether an app runs natively on Apple silicon, choose View > Columns and turn on Kind. It shows Apple for native apps and Intel for apps that run through Rosetta translation.

Apple notes that most of the time your Mac uses only a small share of its processing power. A number that is high for a reason you can name is fine. These are the signs that point to a real problem:

• The app stays high for several minutes while you are not using it.
• It sits at about 100% without moving. That often means one thread is stuck in a loop, using one full core.
• Its CPU Time column keeps climbing quickly while the app sits in the background.
• The fans get louder, the Mac feels warm, or the battery drops faster than usual at the same time.
• The value does not fall after you close the window, document or tab that caused the work.

1. In Activity Monitor, click the CPU tab and sort by % CPU. Watch for a minute so a short spike does not mislead you.
2. If the process is a helper, choose View > All Processes, Hierarchically to see which app it belongs to.
3. Save your work and quit the app normally. If it does not respond, select it and use Force Quit.
4. Open the app again. If the CPU use comes back with nothing to explain it, check for an update from the developer.
5. If it keeps happening, take a sample of the process in Activity Monitor and send it to the developer. It shows what the app was doing.