The cheapest USPS price for a particular dimension and weight

It’s easiest to use our predefined_packages to shop around for USPS rates. If you want to enter your own dimensional values, make sure you have two different shipment objects for a Parcel and an Envelope, as it’s impossible to return Mail rates for a Parcel (and vice versa). For instance, trying to get a First Class Mail rate on a bigger parcel will not qualify.