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When I open Task Manager and Process Explorer I can see they present different CPU utilization values. Moreover, 'Processes' and 'Details' tabs in the same Task Manager indicate different CPU utilization values. I want to understand why, so I tried doing some research.

I have a guess that the difference is because some performance monitors include the CPU speed in their calculations while others don't. To test that theory I created a simple infinite loop in python which does not use IO: while True: pass. This should exhaust the core it is running in, as it does not use IO at all so there is no spare time for the core to idle.

I ran the loop to see the results:

  • Process Explorer: python.exe 8.34%
  • Task Manager's Details tab: python.exe 8%
  • Resource Monitor: Maximum frequency 180%
  • Task Manager's Process tab: python.exe 16.8%
  • Process Explorer CPU usage: 10.28%
  • Resource Monitor: CPU usage 19%
  • Task Manager's Performance tab: CPU utilization 19%

Now let's do some math and explain these values. I am using 12 logical processors with base speed of 2.21GHz, so the results are:

  • Process Explorer: python.exe 8.34%
    • My python program should exhaust a single core. My system has 12 logical cores so 100/12 is approximately 8.34.
  • Task Manager's Details tab: python.exe 8%
    • Same as previous calculation, but task manager rounds the result to 8%.
  • Resource Monitor: Maximum frequency 180%
    • 180% of the base speed is approximately 3.98GHz, which was my CPU speed during the test.
  • Task Manager's Process tab: python.exe 16.6%
    • 180% of 8.34 is 15, which is not exactly 16.6 but pretty close...
  • Process Explorer CPU usage: 10.28%
    • It seems like the 'real' CPU usage without any scale.
  • Resource Monitor: CPU usage 19%
    • 180% of 10.28 is 18.5 which is pretty close
  • Task Manager's Performance tab: CPU utilization 19%
    • Same as in Task Manager Performance tab

It all adds up to be pretty simple: Process Explorer shows the usage of the cpu without any scale, Task Manager and Resource Monitor show it with a scale of the current CPU speed (except for the Details tab for some reason). It also seems like Task Manager cannot show values over 100%, but Resource Monitor can.

I tried it one more time, now with several loops on several cores, so the difference would be more significant:

  • Resource Monitor: Maximum frequency 156%
    • 156% of the base speed is approximately 3.44GHz, which was my CPU speed during the test.
  • Process Explorer CPU usage: 69.57%
    • It seems like the 'real' CPU usage without any scale.
  • Resource Monitor: CPU usage 109%
    • 156% of 69.57 is 108.52 which can be rounded to 109.
  • Task Manager's Performance tab: CPU utilization 100%
    • Same as Resource Monitor, but is capped to 100%

So my question is:
Am I correct? I tried to find any evidence around the web but it seems like no one has done the same math. In fact some people gave contradicting explanations to this difference... Am I missing something?

I've found similar questions in this site, but their answers seem incorrect or irrelevant to my question:

  • Some of them explained that there might be processes from other users. It is not relevant here as I see processes from all users.
  • Some other answers explained that Process Explorer and Task Manager have different polling algorithms. this is fine but it does not explain the different values of Processes and Details tabs of the same Task Manager.
  • Other answers mentioned that there is no connection between CPU usage and CPU speed. As I understand this is wrong because clearly there is a connection (as I showed above), and this connection actually explains the difference. Am I missing something?

The questions I have read:

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  • Did you see this page>>>>medium.com/@ppatali/… Commented Dec 3, 2019 at 21:45
  • @Moab I have read it now, bit it only describes how to use Process Explorer (which I already used in my question) and Process Monitor (which is not relevant to my question) Commented Dec 3, 2019 at 22:40
  • Same issue here. My PC is in near idle state, PE shows < 1%, TM shows around 10% - 20%. I was trying to track what causes my fans to spin and TM seems to better tool for that, whet TM shows > 15%, my fans are audibly up while PE keeps pretending that nothing is happening. Commented Nov 22, 2022 at 18:28
  • Well, my case is quite the opposite. PE shows a lot more CPU than TM (e.g. 100% vs 15%). I seldom open TM, but PE is always running, and sometimes I compare them (especially when %CPU is high, machine slow and laggy), and I see big differences in their numbers… Commented Apr 4, 2025 at 18:56

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Yes — your reasoning is correct.

The differences you observed aren’t random or just polling quirks; they come from how each tool reports CPU usage:

Process Explorer and Task Manager’s Details tab show raw utilization — the percentage of time a logical core is busy. On a 12‑core CPU, one saturated core is about 8%.

Task Manager’s Processes and Performance tabs scale that raw usage by the ratio of current CPU speed to base speed. If turbo boosts a core to ~180% of base, the reported usage doubles to ~16–19%.

Resource Monitor shows both the “Maximum frequency” (current vs base) and scaled CPU usage, which is why it can exceed 100%.

So yes, your math and explanation are right: the discrepancy is due to scaling by turbo frequency versus reporting raw time slices. The only nuance is that Task Manager caps utilization at 100%, while Resource Monitor does not.

Well, my case is quite the opposite. PE shows a lot more CPU than TM (e.g. 100% vs 15%). I seldom open TM, but PE is always running, and sometimes I compare them (especially when %CPU is high, machine slow and laggy), and I see big differences in their numbers… –Alexandre

The discrepancy can go both ways, depending on which tool is applying scaling and how the numbers are normalized. Here’s why you might see Process Explorer (PE) showing much higher CPU than Task Manager (TM):

Process Explorer reports per‑process CPU usage as a percentage of one logical processor. If a process is saturating a core, PE will show ~100% for that process.

Task Manager (Processes tab) divides usage across all logical processors. On a 12‑core system, one fully loaded core looks like ~8%. If turbo scaling is applied, it might show ~15–20%, but still far below the raw 100% that PE shows.

Task Manager (Performance tab) shows overall CPU utilization across the system, capped at 100%.

Details tab in TM is closer to PE, but rounding and sampling differences can still make it look lower.

So in your case, PE is showing the raw “this process is maxing out one core” number, while TM is normalizing that load across all cores, which makes it look smaller. That’s why you see 100% in PE versus ~15% in TM — they’re both correct, but they’re measuring from different perspectives.

Bottom line:

  • PE emphasizes per‑core saturation.

  • TM emphasizes system‑wide distribution.

  • The mismatch is expected, especially on multi‑core CPUs with turbo scaling.

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