How do I find my serial number? I can't find the receipt and all I have is the order number.
You can call apple care at: 1800.275.2273 and have them look up your account by like the phone number or email address it was registered in their system with and they would be able to email you the serial number if it was found in their system.
if you have the original box, it will be on there.
Login to your support profile online. If registered, it will be listed there.
https://daw.apple.com/cgi-bin/WebObjects/DSAuthWeb.woa/wa/classicLogin?appIdKey= 58ef9db8ff4d201409e7270a68e4408ae1678e1618204c476572a1b5e5fb3518&path&language=U S-EN
Retrieving data ...