# Number of CPUs
> Number of CPUs.
## Usage
```javascript
var NUM_CPUS = require( '@stdlib/os/num-cpus' );
```
#### NUM_CPUS
Number of CPUs.
```javascript
var n = NUM_CPUS;
// returns
```
## Notes
- In a web browser, the number of CPUs is determined by querying the hardware concurrency [API][hardware-concurrency].
- Otherwise, the number of CPUs is determined via the [os][node-os] module.
## Examples
```javascript
var proc = require( 'process' );
var cluster = require( 'cluster' );
var NUM_CPUS = require( '@stdlib/os/num-cpus' );
var i;
function onTimeout() {
proc.exit( 0 );
}
if ( cluster.isMaster ) {
for ( i = 0; i < NUM_CPUS; i++ ) {
cluster.fork();
}
} else {
console.log( 'Worker %s. Process id: %d.', cluster.worker.id, cluster.worker.process.pid );
setTimeout( onTimeout, 1000 );
}
```
* * *
## CLI
### Usage
```text
Usage: num-cpus [options]
Options:
-h, --help Print this message.
-V, --version Print the package version.
```
### Examples
```bash
$ num-cpus
```
[node-os]: https://nodejs.org/api/os.html#os_os_cpus
[hardware-concurrency]: https://developer.mozilla.org/en-US/docs/Web/API/NavigatorConcurrentHardware/hardwareConcurrency