Per-process CPU doesn't add up to total in Activity Monitor? Observing Activity Monitor, the per-process CPU is often very different to the total CPU.
Example
Here the sum of individual processes is &gt; 50%, yet the total said to be (100 - 91.43) 8.57%.

Why is this? And which is correct?
The %CPU column is percentage of one [virtual] core. The total summary is percentage of entire CPU. So if, for instance you have 4 real cores, 8 virtual, the maximum possible total figure in the %CPU column would be 800%
if you want to check how many cores you have, Use either Window menu &gt; CPU usage or CPU history.  The number of stripes is the number of virtual [hyper-threaded] cores. Halve that to get your total physical core count.
This shows 12 cores, 24 HT cores…