What Are Letters?


Letters are a written means of correspondence with another person, business entity,  or other organization. A letter can be comprised of an invoice, marketing message, personal note, and any other item that fits into a business-sized envelope.

The USPS provides a simple and affordable way to mail letters using First-Class Mail®. To qualify as a First-Class Mail® letter, your mailpiece must be no smaller than 3½” high x 5” long and at least 0.007” thick. It must be no bigger than 6 1/8″ high x 11½” long and no more than ¼” thick. Letters sent via First Class Mail® cannot weigh more than 3.5 ounces.


To mail a letter, you do not need to visit the Post Office as long as you have postage stamps, access to a postage meter or can print postage online from a company like Stamps.com. Simply address your envelope, affix postage to the upper right corner and drop it in a collection box or hand it to your mail carrier. First-Class Mail® letters sent within the United States generally arrive within 1-3 days.

First Class letters can be insured against loss and damage. You can also add services such as Certified Mail, Collect on Delivery or Certificate of Mailing.

Offer bar image

Try us out for 4 weeks!

Get $5 in free postage to use during your trial.

Sending First-Class Mail® letters with Stamps.com is easy

When you combine the ease of sending First-Class Mail® letters with the convenience of Stamps.com, you and your staff will never have to waste time at the Post Office again. Not only does Stamps.com tell you exactly how much postage is required to send a letter of any weight, shape, or size to any domestic or international destination, but it also lets you print official, USPS-approved postage and address labels from the comfort of your own home or office.

Stamps.com features include:

  • Access to all USPS mail classes.
  • Skip the trips to the Post Office, and print postage online 24/7.
  • Print any denomination of postage on envelopes, labels, or plain paper.
  • Add USPS special services including USPS Tracking®, Return Receipt, Registered Mail, insurance, and more.

$60 in free postage and supplies when you sign up!

  • $5 in free postage added to your account
  • 5 lb digital scale (only pay for S&H)
  • Free mailing and shipping supplies kit
  • Risk-free 30-day trial
  • No long-term contracts. Cancel anytime.