diff --git a/src/Cli.php b/src/Cli.php
index 9fc906f..2ef2183 100644
--- a/src/Cli.php
+++ b/src/Cli.php
@@ -26,6 +26,7 @@
 use Symfony\Component\Console\Output\OutputInterface;
 
 use function JBZoo\Utils\bool;
+use function JBZoo\Utils\int;
 
 /**
  * Class CliHelper
@@ -75,6 +76,8 @@ class Cli
      */
     private int $prevMemory;
 
+    private ?int $numberOfCpuCores = null;
+
     /**
      * @param InputInterface  $input
      * @param OutputInterface $output
@@ -384,4 +387,53 @@ public function isProgressBarDisabled(): bool
     {
         return bool($this->getInput()->getOption('no-progress'));
     }
+
+    /**
+     * @return int
+     * @see https://github.com/phpstan/phpstan-src/blob/f8be122188/src/Process/CpuCoreCounter.php
+     */
+    public function getNumberOfCpuCores(): int
+    {
+        if ($this->numberOfCpuCores !== null) {
+            return $this->numberOfCpuCores;
+        }
+
+        if (!\function_exists('proc_open')) {
+            return $this->numberOfCpuCores = 1;
+        }
+
+        // from brianium/paratest
+        // Linux (and potentially Windows with linux sub systems)
+        if (\is_file('/proc/cpuinfo')) {
+            $cpuinfo = \file_get_contents('/proc/cpuinfo');
+            if ($cpuinfo !== false) {
+                \preg_match_all('/^processor/m', $cpuinfo, $matches);
+                return $this->numberOfCpuCores = \count($matches[0]);
+            }
+        }
+
+        // Windows
+        if (\DIRECTORY_SEPARATOR === '\\') {
+            $process = \popen('wmic cpu get NumberOfLogicalProcessors', 'rb');
+            if (\is_resource($process)) {
+                /** @phan-suppress-next-line PhanPluginUseReturnValueInternalKnown */
+                \fgets($process);
+                $cores = int(\fgets($process));
+                \pclose($process);
+
+                return $this->numberOfCpuCores = $cores;
+            }
+        }
+
+        // *nix (Linux, BSD and Mac)
+        $process = \popen('sysctl -n hw.ncpu', 'rb');
+        if (\is_resource($process)) {
+            $cores = int(\fgets($process));
+            \pclose($process);
+
+            return $this->numberOfCpuCores = $cores;
+        }
+
+        return $this->numberOfCpuCores = 2;
+    }
 }
diff --git a/src/CliCommandMultiProc.php b/src/CliCommandMultiProc.php
index aa714e2..3c65cd5 100644
--- a/src/CliCommandMultiProc.php
+++ b/src/CliCommandMultiProc.php
@@ -24,16 +24,17 @@
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Process\Process;
 
+use function JBZoo\Utils\int;
+
 /**
  * Class CliCommandMultiProc
  * @package JBZoo\Cli
  */
 abstract class CliCommandMultiProc extends CliCommand
 {
-    private const PM_DEFAULT_MAX_PROCESSES = 20;
-    private const PM_DEFAULT_INTERVAL      = 100;
-    private const PM_DEFAULT_START_DELAY   = 1;
-    private const PM_DEFAULT_TIMEOUT       = 7200;
+    private const PM_DEFAULT_INTERVAL    = 100;
+    private const PM_DEFAULT_START_DELAY = 1;
+    private const PM_DEFAULT_TIMEOUT     = 7200;
 
     /**
      * @var array
@@ -56,7 +57,7 @@ protected function configure(): void
                 null,
                 InputOption::VALUE_REQUIRED,
                 'Process Manager. The number of processes to execute in parallel (os isolated processes)',
-                self::PM_DEFAULT_MAX_PROCESSES
+                'auto'
             )
             ->addOption(
                 'pm-interval',
@@ -137,8 +138,19 @@ protected function executeAction(): int
      */
     protected function executeMultiProcessAction(): int
     {
+        $procNum = $this->getNumberOfProcesses();
+        $cpuCores = $this->helper->getNumberOfCpuCores();
+        $this->_("Max number of sub-processes: {$procNum}", OutLvl::DEBUG);
+        if ($procNum > $cpuCores) {
+            $this->_(
+                "The specified number of processes (--pm-max={$procNum}) "
+                . "is more than the found number of CPU cores in the system ({$cpuCores}).",
+                OutLvl::WARNING
+            );
+        }
+
         $procManager = $this->initProcManager(
-            $this->getOptInt('pm-max') ?: self::PM_DEFAULT_MAX_PROCESSES,
+            $procNum,
             $this->getOptInt('pm-interval') ?: self::PM_DEFAULT_INTERVAL,
             $this->getOptInt('pm-start-delay') ?: self::PM_DEFAULT_START_DELAY
         );
@@ -343,4 +355,21 @@ private function getMaxTimeout(): int
     {
         return $this->getOptInt('pm-max-timeout') ?: self::PM_DEFAULT_TIMEOUT;
     }
+
+    /**
+     * @return int
+     */
+    private function getNumberOfProcesses(): int
+    {
+        $pmMax = \strtolower($this->getOptString('pm-max'));
+        $cpuCores = $this->helper->getNumberOfCpuCores();
+
+        if ($pmMax === 'auto') {
+            return $cpuCores;
+        }
+
+        $pmMaxInt = \abs(int($pmMax));
+
+        return $pmMaxInt > 0 ? $pmMaxInt : $cpuCores;
+    }
 }
diff --git a/tests/Cli/CliMultiProcessTest.php b/tests/Cli/CliMultiProcessTest.php
index bb16089..55dc3d2 100644
--- a/tests/Cli/CliMultiProcessTest.php
+++ b/tests/Cli/CliMultiProcessTest.php
@@ -30,7 +30,7 @@ public function testAsRealExecution()
         $start = microtime(true);
         $result = Helper::executeReal(
             'test:sleep-multi 123 " qwerty "',
-            ['sleep' => 1, 'no-progress' => null],
+            ['sleep' => 1, 'no-progress' => null, 'pm-max' => 50],
             'JBZOO_TEST_VAR=123456'
         );
 
@@ -61,7 +61,7 @@ public function testAsRealExecution()
     public function testAsVirtalExecution()
     {
         $start = microtime(true);
-        $result = Helper::executeVirtaul('test:sleep-multi', ['sleep' => 1, 'no-progress' => null]);
+        $result = Helper::executeVirtaul('test:sleep-multi', ['sleep' => 1, 'no-progress' => null, 'pm-max' => 5]);
         $time = microtime(true) - $start;
 
         $outputAsArray = json($result)->getArrayCopy();
@@ -88,7 +88,10 @@ public function testAsVirtalExecution()
     public function testException()
     {
         $start = microtime(true);
-        $result = Helper::executeReal('test:sleep-multi 123 456 789', ['sleep' => 2, 'no-progress' => null]);
+        $result = Helper::executeReal(
+            'test:sleep-multi 123 456 789',
+            ['sleep' => 2, 'no-progress' => null, 'pm-max' => 5]
+        );
         $time = microtime(true) - $start;
 
         $outputAsArray = json($result[1])->getArrayCopy();
@@ -112,4 +115,19 @@ public function testException()
 
         isTrue($time < 5, "Total time: {$time}");
     }
+
+    public function testNumberOfCpuCores()
+    {
+        $result = Helper::executeReal(
+            'test:sleep-multi 123 " qwerty "',
+            ['sleep' => 1, 'no-progress' => null, 'pm-max' => 50, '-vvv' => null]
+        );
+
+        isContain('Debug: Max number of sub-processes: 50', $result[1]);
+        isContain(
+            'Warning: The specified number of processes (--pm-max=50) '
+            . 'is more than the found number of CPU cores in the system',
+            $result[1]
+        );
+    }
 }