Why doesn't the "% CPU" in System Monitor add up to 100? (% CPU is the third column on the following screenshot)

cpu time

3 Answers 3


Two reasons:

  1. The calculations are per-core. So if you have a dual-core system then the maximum will be 200%.
  2. You will not necessarily see all processes which are using your CPU in System Monitor, so the CPU usage might be below 100% for each processor.

Furthermore it is unusual for 100% of any processor to be in use. See the resources tab for the total in use per processor.

  • 1
    Ah ok, I'm on a dual core that's why! A bit unintuitive though. Thx. Dec 5, 2010 at 1:22

Does your do you have more than one CPU core? Or Hyper-Threading (or the AMD equivalent)?

You can see how many CPUs Ubuntu thinks you have by running this:

cat /proc/cpuinfo | grep "^vendor" | wc -l

Ubuntu will count each of these. So if you have 8 CPU's (as I do, quad-core with hyperthreading), you can reach 800% CPU.


There is more information regarding this issue at the askubuntu link below (a question I asked):

'htop' does not show the correct CPU%, but 'top' does.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.