Many Facebook Applications need Facebook Page ID and Profile ID or Admin ID. If you are using a custom username for your Facebook profile or page,e.g facebook.com/PixelInsert then unique ID will not appear. Facebook social plugins require this unique ID
1. Facebook Graph API
Facebook Graph API help detecting Facebook Page/Profile/Admin ID from your Facebook username
https://graph.facebook.com/yourusername
You will get the following details in JSON format. Here you can find the ID in the first line.
2. Facebook URL address
You’ll see the unique ID at the end of your facebook URL address if you don’t setup facebook username
http://www.facebook.com/profile.php?id={YOU_FACEBOOK_ID}