How to know Facebook ID from mobile number

First of all login to your Facebook account by opening the Facebook App.

Now go to Menu and click on Settings.

Now a new page will open, after that scroll down and go to the option of Contact Uploading, and click on it.

If contact uploading is off, then turn it on.

Now on the screen you will see the option of Facebook Friends, turn it on.

After this all your contact numbers start uploading on Facebook.

In no time whatever your friends and relatives are on Facebook will start showing you.