diff --git a/rainbows_config.rb b/rainbows_config.rb
index ff01a2e9..971753ef 100644
--- a/rainbows_config.rb
+++ b/rainbows_config.rb
@@ -1,9 +1,27 @@
+def processor_count
+  case RbConfig::CONFIG['host_os']
+  when /darwin9/
+    `hwprefs cpu_count`.to_i
+  when /darwin/
+    ((`which hwprefs` != '') ? `hwprefs thread_count` : `sysctl -n hw.ncpu`).to_i
+  when /linux/
+    `cat /proc/cpuinfo | grep processor | wc -l`.to_i
+  when /freebsd/
+    `sysctl -n hw.ncpu`.to_i
+  when /mswin|mingw/
+    require 'win32ole'
+    wmi = WIN32OLE.connect("winmgmts://")
+    cpu = wmi.ExecQuery("select NumberOfCores from Win32_Processor") # TODO count hyper-threaded in this
+    cpu.to_enum.first.NumberOfCores
+  end
+end
+
 Rainbows! do
   use :ThreadPool
 
   client_max_body_size 100*1024*1024 # 100 Megabytes
 
-  worker_processes 8
+  worker_processes processor_count
   worker_connections 32
   timeout 10