diff --git a/.npmignore b/.npmignore
index a1946909..387fcfc1 100644
--- a/.npmignore
+++ b/.npmignore
@@ -13,3 +13,5 @@ coverage/
 
 .yaspellerrc
 docs/
+
+benchmark
diff --git a/benchmark b/benchmark
new file mode 100755
index 00000000..0319be05
--- /dev/null
+++ b/benchmark
@@ -0,0 +1,13 @@
+#!/usr/bin/env node
+
+var nanoid = require('./')
+var generate = require('./generate')
+
+var start = Date.now()
+for (var i = 0; i < 100000; i++) {
+  nanoid()
+  generate('1234567890abcdef', 10)
+}
+var end = Date.now()
+
+process.stdout.write(end - start + ' ms\n')
diff --git a/format.js b/format.js
index d3d43520..4c0f0d53 100644
--- a/format.js
+++ b/format.js
@@ -24,10 +24,12 @@
  * @name format
  */
 module.exports = function (random, alphabet, size) {
+  var step = Math.ceil(1.2 * 256 / alphabet.length * size)
+
   var bytes, byte
   var id = ''
   while (id.length !== size) {
-    bytes = random(size)
+    bytes = random(step)
     for (var i = 0; i < bytes.length; i++) {
       byte = bytes[i]
       if (byte < alphabet.length) {
@@ -36,6 +38,7 @@ module.exports = function (random, alphabet, size) {
       }
     }
   }
+
   return id
 }