We often get this question from customers, especially brides. Here are some guidelines from the United States Postal Service
First-Class letter dimensions:
|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.|
So, what does that mean? Unless you have a postal scale it may be difficult to determine on your own so take a sample of what you are mailing to the Post Office and they will be able to tell you the exact postage.