The First Class postal rates between the United States and United Kingdom are between $1.15 and $4.11 for letters and between $2.29 and $35.08 for large envelopes or flat packages. Packages are priced at between $6.55 and $38.95.
The weight of a package is the primary factor in determining how much it costs to ship. Prices are assessed on a not-over basis, which means that all weights are rounded down to the nearest ounce and priced accordingly. There is a weight limit of four pounds on packages being shipped First Class. Any items that weigh more must be shipped using a different method.