I need to calculate real time shipping costs of the orders of the project I'm currently working on.
I have the dimensions and weights of packages and US shipping address.
Orders are only placed within US
Can you suggest me what options I have. Thanks
A database of known values for varying size-ranges is what I'd do. And then match against that. Of course, it'll also need to consider the shipping company.
Most shipping vendors, including FedEx and the Post Office, expose web services that can be used to extract rate information. You may need to get "certified" if you release your software commercially, but generally don't need to do much but run a few tests on their test server (for your own sanity) if it's just for an internal, line of business app.
There are some libraries available, like proprietary/commercial DotNetShip, but now FedEx has WSDL and the USPS interface isn't that hard to use.