Per-process CPU doesn't add up to total in Activity Monitor?
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…