Postcards are an inexpensive way to get an immediate message to customers. When they arrive in the mail, there’s the message -- no envelope to open! First-Class Mail postcards are a great value, too. With First-Class Mail postcards, you pay a low price and get all of the benefits, like forwarding and return that come with First-Class Mail. And, if you mail with single-piece First-Class Mail postage affixed, there is no extra work involved -- simply drop the postcards in a collection box.

You may think that your mailpiece is a "postcard," because it is a single sheet of paper. But to qualify for mailing at the First-Class Mail postcard price, it 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 inches thick

If your mailpiece does not meet the dimensions above, then the Postal Service considers it a letter and letter-size postage is charged. With Standard Mail, there is a little more flexibility -- there is no separate (lower) price for postcards, so you don't have to worry about your postcard being too big -- because you're paying letter prices anyway. But make sure that your postcard is no larger than 6-1/8" x 11-1/2" x 1/4" thick. Mailpieces larger than any of those dimensions and you'll have to pay flats (large envelope) postage prices.

Some mailers want to attach stickers, magnets, or other items to their postcards. However, an attachment may disqualify the mailpiece for mailing at the First-Class Mail postcard price—or even make it nonmailable. The rules about attachments to postcards are restrictive, so check with your mailpiece design analyst (MDA)[1] or business mail entry staff[2], who can tell you if your mailpiece design will be mailable.

TIPS
-If you’re planning to mail a postcard, First-Class Mail gives you the best value for your postage dollars. There is no lower postcard price in Standard Mail.
-0.007 inches? How do I measure that? As a guide, an index card is thick enough. If in doubt, contact a mailpiece design analyst (MDA)[4] at the Post Office near you. MDAs have tools for precisely measuring thickness and can tell you if your mailpiece is thick enough.
-Make sure your mailpiece meets the minimum thickness requirement. Thin, flimsy pieces tend to get caught in mail processing equipment. If your mailpiece gets damaged in the equipment, then your message doesn’t reach your customers.
-What is high? What is long? Length is the side parallel to the address. Height is the side that is perpendicular to the length.

Sizes for letters[5]

Sizes for flats[6]

Sizes for parcels[7]