Postal Letter

What is the minimum size envelope that can be mailed with usps?

I'm mailing a mass amount of very small cards.... What is the smallest size the post office will accept? The USPS website was very disappointing.

Public Comments

1. when you say small cards do you mean a small greeting card like a birth announcement (in an envelope) or do you mean a post card? First-Class letter dimensions: Rectangular At least 3-1/2 inches high X 5 inches long X .007 inch thick No more than 6-1/8 inches high X 11-1/2 inches long X 1/4 inch thick Maximum weight is 3.5 ounces Letters that are considered nonmachinable are subject to a surcharge. Length is the dimension parallel to the address. To qualify for First-Class Mail card rates, a card must be: • Rectangular • At least 3-1/2 inches high X 5 inches long X 0.007 inch thick • No more than 4-1/4 inches high X 6 inches long X 0.016 inch thick Length is the longest dimension parallel to the address. Oversized cards will be charged as a letter or large envelope depending on the size.
2. As stated above... the USPS website is quite clear, thank you!