User281315223 posted
Have you tried visiting the
FedEx Developer Resource center?
I'm sure that FedEx has an API available for handling things like this although
based on this, you'll probably need to sign up for a FedEx account in order to access the available documentation / web services.
If you don't want to deal with that yourself, I would recommend visiting this
GitHub Repository for the DotNetShipping Project. It appears to be a wrapper that can handle shipping calculations for FedEx, UPS and the United States Postal Service and I am sure that it would be much easier to implement that doing it on your own. Additionally,
it looks like there is even a
NuGet package available for it, to easily implement it into your application.