Usps First Class Letter Size. The longest side of the parcel girth: Within, across, and between the united states.
3,277 views message 4 of 12 0 helpful reply. Larger sizes are allowed in different first class mail categories. And flats up to 13 oz.
All postcards and envelopes (or flats) must be rectangular, otherwise an additional charge may apply.
If the mailpiece falls within these dimensions, it is classified as a letter. In weight.you can send things like cards, brochures, and lightweight merchandise. See step 3 for details. If the mailpiece falls within these dimensions, it is classified as a letter.