[HOW TO] Get the Number of CPU Cores in an Android Device

While developing the latest release of Micro CPU Monitor, I ran into difficulties trying to determine the number of cores in a mobile device. In the past I’d been using /proc/stat to get CPU usage for the whole system (all processors and cores combined). After reading this article (including the comments) and playing around a bit in bash, I discovered this same file could also be used to get CPU usage for each processor/core separately.

But it turns out that a lot of multi-core Android devices actually switch the cores on and off independently, in order to save power. On my dual core Galaxy S II, /proc/stat will sometimes only show CPU usage for a single core. At other times, it will show both cores. So this makes it pretty much impossible to use /proc/stat to calculate a reliable figure for the number of cores.

After a lot more fiddling (and thanks to the feedback of several devs on Google+) I managed to come up with a solution. To count the number of cores, I just needed to enumerate the CPU devices in /sys/devices/system/cpu/. From my research, it seems that this directory is readable from any Android app - even without root.

Here’s a simple function which uses this method to return the total number of CPU cores for the system. On a desktop OS there could be some confusion between physical and virtual CPUs, but on Android it’s pretty simple. At this stage, there are only really dual-core and quad-core devices out there, so we can get an accurate figure just by counting the virtual devices like this.


  • Gets the number of cores available in this device, across all processors.

  • Requires: Ability to peruse the filesystem at “/sys/devices/system/cpu”

  • @return The number of cores, or 1 if failed to get result
    private int getNumCores() {
    //Private Class to display only CPU devices in the directory listing
    class CpuFilter implements FileFilter {
    public boolean accept(File pathname) {
    //Check if filename is “cpu”, followed by a single digit number
    if(Pattern.matches(“cpu[0-9]+”, pathname.getName())) {
    return true;
    return false;

    try {
    //Get directory containing CPU info
    File dir = new File("/sys/devices/system/cpu/");
    //Filter to only list the devices we care about
    File[] files = dir.listFiles(new CpuFilter());
    Log.d(TAG, "CPU Count: "+files.length);
    //Return the number of cores (virtual CPU devices)
    return files.length;
    } catch(Exception e) {
    //Print exception
    Log.d(TAG, “CPU Count: Failed.”);
    //Default to return 1 core
    return 1;

I hope this code will be helpful for any other devs out there who are in a similar situation. I’d definitely welcome any feedback as well - if you’ve got a different approach or some comments, I’d be happy to hear them!

Now… back to my coding :cool:

As a user pointed out on Stack Overflow, the original version of this code used a regular expression “cpu[0-9]” which only recognises up to 10 CPUs. That was an oversight on my behalf - mainly because I don’t have any devices with more than 4 cores to test it on! I’ve now updated the post to use a more flexible “cpu[0-9]+”, which can handle any number of CPUs.

You might this useful:


Returns the number of processor cores available to the VM, at least 1. Traditionally this returned the number currently online, but many mobile devices are able to take unused cores offline to save power, so releases newer than Android 4.2 (Jelly Bean) return the maximum number of cores that could be made available if there were no power or heat constraints.

This is the type of posts we need in this forum.
I recently needed something similar as we were facing some problems with older devices.
Thanks for sharing you really saved the day.