When sending bulk mail, it's important to know which mail classification your mailpieces fall into. Here are some basic rules of thumb for letters, flats and parcels.
To qualify as a letter, a mail piece must range from 3 1/2" x 5" to 6 1/2" x 11 1/2". This category usually includes postcards, letters (inserted into envelopes), and newsletters (folded to appropriate size and tabbed).
A flat, also referred to as a large envelope, must range between 6 1/8" x 11 1/2" and 12" x 15" to quality as First-Class Mail. The thickness must also be between 1/4" and 3/4". Flats cannot be rigid or any shape other than a rectangle. Newsletters and magazines also quality as flats.
Letters that weigh more than 3.5 ounces, or are thicker than ¼ of an inch, are not eligible to be presorted as letters and will qualify as flats. PPS can presort your flats if postage is not applied, and we will invoice you for the postage. If you apply postage to your flats and parcels, you must apply the full rate postage.
If your mailpiece does not classify as a letter or a flat, then it is a parcel. While typically slower to ship, parcels offer great cost savings.
Depending on the size, there are generally three types of parcels: