You can save box and case dimensions and weights to your account for easy future use in two ways.

Prior to shipping:
1) Log in to your account
2) Click your name
3) Go to "Your Boxes"
4) Click "Add a new box" then enter and save details about your box or case

Or, to save your boxes and cases automatically whenever you enter them while booking future shipments:
1) Log in to your account
2) Click your name
3) Select "Account Home"
4) Select "Account Details"
5) Select "Edit"
6) Select " Save packages, addresses and payment methods when I purchase"
7) Click "Save"