Minimum Size

• A postcard's dimensions must be a minimum of 3 1/2 inches high by 5 inches long by 0.007 inches thick. Any mail under this size is not accepted by the USPS.
  
  

Maximum Size

• The maximum size of a postcard is 4 1/4 inches high by 6 inches long by 0.016 inches thick.
  
  

Shape

• A postcard must be rectangular in shape in order to qualify for first class mail service.
  
  

Cost

• Postcards meeting the size requirements cost around 20 cents less than those that exceed the size requirements.
  
  

Considerations

• If a postcard fails to meet size and shape requirements, it is charged the same mailing fee as a first-class letter or large envelope.
  
  

Options

• Postcards can be sent with a Certificate of Mailing, which proves that the card was mailed, or they can be sent as Certified Mail, giving the sender a receipt and the ability to track delivery.
  
  

First Class Mail

• First class mail is delivered within 1 to 3 days of mailing.