How many CPU cores does my browser report?
That number counts threads, not cores. A four core chip with hyper-threading reports 8, which is why the figure often looks twice as generous as your processor's specification sheet. It is also a ceiling the browser chooses rather than a hardware readout: Safari caps it, and Tor Browser reports 2 to everybody.
What this number actually means
The number above is navigator.hardwareConcurrency, which MDN defines as the number of logical processors available to run threads on your computer. Logical processors, not physical cores. If your chip supports hardware multithreading (Intel calls it Hyper-Threading, AMD calls it SMT) each physical core presents two logical processors, so an 8 core chip usually reports 16. There is no web API that reveals the physical core count, so no website, including this one, can tell you that number.
The number of logical CPU cores your browser reports is shown above, from the hardwareConcurrency value. It reflects logical processors, so a chip with hardware multithreading may report double its physical core count. It tells a page how many parallel workers it can reasonably spin up.
Web apps use this to decide how many background threads (Web Workers) to create for heavy tasks like image processing, compression or parsing, so the work spreads across cores instead of freezing the interface. Ask for too many workers on a small device and you slow things down; too few on a big one wastes capacity.
The figure is a hint, not a guarantee of exclusive access. Your cores are shared with everything else running, and some browsers cap or round the number, so treat it as an upper bound for parallelism rather than a precise hardware spec.
How a website reads this
This is the exact call a page makes. Nothing else is involved, and nothing is sent anywhere: the value is read in your browser and displayed to you.
navigator.hardwareConcurrencyThe number of parallel workers the browser is willing to run, which is a count of logical processors and not of physical cores. On a chip with simultaneous multithreading it is typically twice the physical core count. The specification explicitly allows a browser to report a lower number than the truth, and Safari and Tor Browser both do.
- Needs your permission
- No, it is read silently
- Can it be faked
- Partly. A page cannot change it, but the browser is permitted to under-report, and privacy browsers cap it at a low fixed number so their users all look alike.
- Contribution to a fingerprint
- About 1.8 bits, our own estimate. Our estimate. Common counts such as 4, 8, 12 and 16 dominate heavily, so most visitors land in a handful of large buckets and only unusual counts stand out. How we estimate this.
What each browser does with it
The same call does not give the same answer everywhere. Several browsers withhold, round or cap this value on purpose, so a blank or suspiciously round result is usually a privacy decision rather than a fault.
| Browser | What it reports |
|---|---|
| Chrome, Edge and other Chromium browsers | Report the logical processor count as the operating system sees it. |
| Firefox | Reports the logical processor count; with resistFingerprinting on, reports 2. |
| Safari | Caps the reported value, so high core-count Macs report a lower number than the hardware has. |
| Tor Browser | Reports 2 for every user. |
Is my core count normal?
Compare what your browser reported with the counts these machines report. If yours looks doubled, that is multithreading, not an error.
| Kind of machine | Typically reports | Why |
|---|---|---|
| Budget laptop or Chromebook | 2 to 4 | Dual or quad core with no multithreading, or a low power chip where the browser sees exactly the physical cores. |
| Mainstream laptop | 8 to 12 | A 4 to 6 core chip with two threads each, or a hybrid design mixing performance and efficiency cores. |
| Mainstream desktop | 12 to 24 | 6 to 12 physical cores with multithreading. This is where the doubled number surprises people most. |
| Workstation or high core count desktop | 16 (Firefox) or the real count (Chrome) | Firefox caps the reported value at 16, so a 32 thread machine reports 16 there and 32 in Chrome. |
| Any Mac in Safari | 8 at most | WebKit clamps the value, reported as a maximum of 8 on macOS, regardless of how many cores the chip really has. |
| Any iPhone or iPad in Safari | 2 | WebKit clamps iOS to 2 to limit hardware fingerprinting, even on chips with far more cores. |
| Tor Browser or Firefox with resistFingerprinting | 2 | The value is fixed at 2 on purpose so every user looks identical. |
Hybrid chips complicate the picture further: a design with 8 performance cores and 16 efficiency cores may report a total that maps onto no simple cores times threads sum.
How many threads does my CPU have?
For most people the answer is the number at the top of this page. Threads and logical processors are the same thing, and hardwareConcurrency reports logical processors, so the value you just saw is your thread count as your browser sees it.
The distinction that matters is between physical cores and threads. A physical core is a real execution unit etched into the silicon. A thread, or logical processor, is a queue of work the operating system can schedule onto a core. With Hyper-Threading or SMT one physical core keeps two queues busy, which is why an 8 core chip shows up as 16 threads: not 16 cores pretending to be 8, but 8 cores presenting 16 lanes.
So if you searched for threads, this number is what you wanted. If you searched for physical cores, halve it as a first guess on a multithreaded chip, then confirm with your operating system as described below, because hybrid chips and clamped browsers both break that rule of thumb.
How do I check my real CPU core count outside the browser?
On Windows, open Task Manager with Ctrl plus Shift plus Escape, go to Performance and select CPU. The panel lists Cores and Logical processors as two separate figures, which is the clearest confirmation of the split described above. System Information (msinfo32) shows the same thing in text form.
On macOS, hold Option and choose Apple menu then System Information, then Hardware. Apple Silicon Macs list the total number of cores and the split between performance and efficiency cores. The terminal command sysctl -n hw.physicalcpu hw.logicalcpu prints both numbers directly.
On Linux, run lscpu. Read the Core(s) per socket, Socket(s) and Thread(s) per core lines; physical cores are cores per socket multiplied by sockets, and logical processors are that multiplied by threads per core. The CPU(s) line at the top is the logical count, the same figure your browser reports.
These operating system tools are the authority. A browser only ever sees what its vendor decided to expose, so where the two disagree, believe your operating system.
Why does my browser report the wrong number of cores?
Three separate things distort the value, and all of them are deliberate. The first is multithreading, which doubles the number relative to physical cores. That is not a distortion so much as a misreading, but it accounts for most of the surprise.
The second is capping. Firefox limits hardwareConcurrency to 16 no matter how many logical processors you have. WebKit clamps harder, with a reported maximum of 8 on macOS and 2 on iOS, chosen specifically to reduce what fingerprinting scripts can learn from Apple hardware. Chromium browsers on desktop generally report the real logical count.
The third is privacy hardening. Firefox with privacy.resistFingerprinting, which is how Tor Browser ships, reports a fixed 2 for everybody. That is the feature working: a value that is the same for every user carries no identifying information at all.
On top of all this the specification itself hedges. MDN notes the browser may report fewer logical cores in order to reflect how many workers can actually run at once, and warns against treating the value as an absolute measurement of the cores in the machine.
What can a website learn about me from my core count?
On its own, very little. Values cluster hard around 4, 8, 12 and 16, so millions of people share yours and knowing it does not single you out.
It becomes useful to a tracker when it is combined. Core count plus device memory plus the WebGL renderer string plus your screen resolution and timezone start to describe one specific machine rather than a class of machines, and none of those signals requires a cookie or a permission prompt. That is the whole idea behind browser fingerprinting: a lot of individually harmless numbers multiplied together.
An unusual value is worth more to a tracker than a common one. Reporting 2 in a desktop browser, or 24, puts you in a much smaller bucket than reporting 8. This is exactly why WebKit clamps and why resistFingerprinting pins the value: pushing everyone into the same bucket destroys the signal.
The honest summary is that you cannot hide your core count in an ordinary browser, and blocking it is not worth much on its own. If you care about the combination, the useful move is a browser that normalises the whole set of signals rather than one of them.
What you should know
Why sites collect it
Performance-sensitive sites read the core count to size their thread pools, parallelising heavy work to keep the interface smooth. Analytics may record it as a rough device-class indicator.
Privacy implications
Core count is a moderate fingerprinting signal. Common values (4, 8, 16) are widely shared, but the number still adds entropy, and unusual counts stand out. It is often combined with device memory and GPU to characterise a device.
How to change or hide it
There is no user-facing setting to change the reported core count. Privacy browsers may cap or normalise it to a common value to reduce distinctiveness. Otherwise it reflects your real logical processor count.
Frequently asked questions
Why does my core count seem too high?
It reports logical processors, so hardware multithreading can make a chip appear to have twice its physical cores. An 8-core chip with two threads each may report 16.
How many threads do I have?
The number at the top of this page. Threads and logical processors are the same thing, and that is what hardwareConcurrency reports, so your browser has already told you.
How many physical cores do I have?
No web API exposes that, so no website can tell you. On a chip with Hyper-Threading or SMT it is usually half the number shown here, but confirm it in Task Manager on Windows, System Information on macOS, or lscpu on Linux.
Why does Safari say I have 8 cores when I have more?
WebKit clamps the reported value, at a maximum of 8 on macOS and 2 on iOS, to limit hardware fingerprinting. Firefox caps it at 16. Chromium browsers on desktop usually report the real logical count.
Does a high core count make websites faster?
Only if a site is built to use multiple workers. Many are single-threaded, so extra cores help heavy web apps but not ordinary pages.
Sources
Browser behaviour changes and vendors cap these values differently, so the claims above that are not self-evident are checked against the specifications and vendor documentation below.
Last checked on . How these values are measured and estimated is set out on the methodology page.
Something wrong here? Tell us what your browser reports and it gets corrected.