How many characters can you squeeze into a Apple Push Notification?

Question

Given that you have a super simple notification such as

{
"aps": { 
    "alert" : <MY_MESSAGE>
     }
}

and the 256 byte limit to deal with how many characters can MY_MESSAGE be? Or the related question could be phrased as, how many bytes are in each character?

Is it as simple as assuming UTF-8 encoding which adds up to 18 bytes worth of non content characters in my example?

Answer 1

Empirically, the alert box will let you have 141 character before truncating the rest of the message. The full message can be much larger than that but for my purposes I only need the alert box limit.

Update for iOS 5

If the new style of list view notifications is enabled, you get about 62 characters.