What is the smallest size letter you can mail

According to the United States Postal Service (USPS), the smallest size letter that can be mailed is a "letter" size, which is defined as:

This size is also known as a "standard letter" or "regular letter" size. Letters that meet these dimensions can be mailed at the standard letter rate, which is currently $0.55 for a 1-ounce letter.

However, if you want to mail a smaller item, you can use a "large envelope" or "flat" size, which has the following dimensions:

Large envelopes can be mailed at a higher rate than standard letters, depending on their size and weight.

It's worth noting that the USPS also has specific rules for mailing items that are smaller than a standard letter, such as postcards, greeting cards, and catalogs. These items have their own specific size and weight requirements, and may be subject to different rates and regulations.