What Types of First-Class Mail Are There?

First-Class Mail is a USPS mail class designed to deliver letters quickly and cost-effectively.

It’s the best choice for organizations mailing documents containing personalized business correspondence, such as statements, trade confirms, and invoices, among others.

But what types of First-Class Mail are there?

And which should you choose for your organization?

Read on to see our breakdown of the types of First-Class Mail the USPS offers.

What Does First-Class Mail Mean?

It’s helpful to explore what this mail category is and the contexts in which it is used. This will allow us to dive deeper into the individual types of First-Class Mail later in the blog.

What Is First-Class Mail?

First-Class Mail is a primary mail category offered by the United States Postal Service for time-sensitive correspondence and lightweight packages. It is commonly used for personal letters, bills, statements, legal notices, and other documents where reliable delivery and the use of forwarding services are important.

What Are the Features of First-Class Mail?

All types of First-Class Mail come with many benefits for the mailing organization. Some of these benefits include:

• Expedited delivery. Letters typically arrive at their destinations in 1–5 business days, depending on distance.

• Forwarding service if the recipient has moved and filed a change of address. While those using any mail class can purchase ancillary service endorsements, First-Class Mail is one of the mail categories that includes automatic forwarding when possible.

• Return service if the mailpiece is undeliverable. Like with forwarding service, this feature is available for an extra charge in many mail classes, but First-Class Mail offers it for free.

• Consistent processing standards across USPS facilities. First-Class Mail is generally processed ahead of certain other mail classes, such as Marketing Mail.

What Are the Weight and Format Limits of the Types of First-Class Mail?

The following materials can be sent as First-Class Mail:

• Letters (standard envelopes).

• Flats (large envelopes, which are over 6 1/8 in height, over 11 1/2 inches long, or over 1/4 inch thick).

Letters have a weight limit of 3.5 oz, while flats have a weight limit of 13 oz.

What Are the Differences Between First-Class Mail and Marketing Mail?

Marketing Mail is primarily for advertising and promotional materials, but First-Class Mail is intended for correspondence that contains personal, transactional, or regulated content. All types of First-Class Mail are processed with priority and include forwarding and return services at no additional charge.

What Are Some Examples of First-Class Mail?

Many documents must be sent as First-Class or Priority Mail. This includes:

• Handwritten or typewritten materials.

• Bills.

• Statements.

• Invoices.

• Personal correspondence.

• Personalized business correspondence.

• Any material that is closed against inspection.

This means that the following types of documents, among others, are often sent as First-Class Mail:

• Billing statements.

• Financial correspondence.

• Legal notifications.

• Insurance documents.

• Appointment reminders.

• Official government communications.

Organizations for whom delivery accuracy and regulatory compliance are important often choose one of the types of First-Class Mail for their mailings.

What Are The Types of First-Class Mail?

First-Class Mail can be broken up into several categories depending on certain factors, such as the envelope used and the mail preparation process.

What Are The Types of First-Class Mail Envelopes?

First-Class Mail can be sent as either letters or flats.

What Are The Types of First-Class Mail Preparation?

Organizations can prepare their mailings as:

• Presorted First-Class Mail.

• Automation First-Class Mail.

• Non-Automation First-Class Mail.

What Are First-Class Mail Letters?

First-Class Mail letters are the most commonly used of the types of First-Class Mail. They are designed for standard-sized envelopes that meet specific dimensional, weight, and machinability requirements established by the USPS.

Letters are cost-efficient and operationally streamlined, as long as the content being mailed fits inside a letter-size envelope.

What Are the Dimensional and Weight Requirements of First-Class Mail Letters?

To qualify as a First-Class Mail Letter, a mailpiece must generally:

• Be rectangular.

• Be a minimum of 3 1/2 inches high, 5 inches long, and 0.007 inches thick, and a maximum of 6 1/8 inches high, 11 1/2 inches long, and 1/4 inch thick.

• Stay within the applicable weight limit of 13 ounces.

Letters that exceed thickness, rigidity, or aspect ratio standards may be classified as nonmachinable, resulting in additional postage.

What Makes First-Class Letters Machinable?

Machinability helps all types of First-Class Mail, including First-Class letters, achieve discounted rates.

In order to qualify as machinable, letters must:

• Be flexible.

• Contain no rigid items.

• Avoid uneven thickness.

• Meet barcode placement requirements.

• Meet the size requirements listed above.

Some issues that trigger nonmachinable surcharges include:

• Clasps or buttons.

• Excessive stiffness.

• Lumpy enclosures.

• Square envelopes.

Processing First-Class letters on automated sorting equipment saves the USPS money and time. This incentivizes them to offer discounted rates to organizations that prepare their mailings in ways that allow for this processing. Machinability is one of the requirements to obtain automated rates, which is why creating machinable mailings is important.

What Are Examples of First-Class Mail Letters?

First-Class letters are the most common format choice for businesses mailing high volumes of documents. Some documents that are often sent as First-Class letters include:

• Monthly billing statements.

• Financial account summaries.

• Insurance policy updates.

• Legal correspondence.

• Trade confirmations.

• Healthcare appointment reminders.

• Healthcare explanation of benefits (EOBs).

• Government notices.

These documents are common types of First-Class Mail letters because they are time-sensitive and contain personalized business information.

What Are First-Class Mail Flats?

A flat is, simply put, a larger envelope. Flats are the larger of the two types of First-Class Mail containers. A mailpiece is classified as a flat when it exceeds letter-size dimensions but still falls within the weight and size standards established by the USPS for First-Class Mail.

Flats are often used when document sets are too large or too thick to qualify as letters but do not justify parcel classification.

They are also used when organizations send important documents unfolded. Flats are large enough to fit a letter-sized sheet of paper without folding.

One advantage of flats is that they allow for the mailing of larger or non-foldable mailpieces in a professional format. One disadvantage is that flats generally cost more than letters.

When Does a Mailpiece Become a Flat?

A piece transitions from a letter to a flat when it exceeds one or more letter thresholds, including:

• A height of 6 1/8 inches.

• A length of 11 1/2 inches.

• A thickness of at least 1/4 inch.

What Requirements Must All Types of First-Class Mail Flats Meet?

Flats must meet certain requirements to avoid parcel qualification, including:

• Maximum height of 12 inches high.

• Maximum of 15 inches long.

• Maximum of 3/4 inches thick.

• No clasps, strings, buttons, or other protrusions.

• Uniform thickness, free from creases, folds, and tears.

Pieces that do not meet these standards may be reclassified as packages, and shipped at the elevated USPS Ground Advantage rate.

What Are Examples of First-Class Mail Flats?

Flats are one of the types of First-Class Mail frequently used by organizations in highly-regulated industries to send compliant mailings. They are able to hold more materials than letters can. Because of this, they can be used for multi-page or oversized correspondence, such as:

• Insurance policy packets.

• Loan documentation packages.

• Legal disclosures.

• Compliance notices.

• Annual reports.

• Financial prospectuses.

• Educational transcripts.

• And any other document or set of documents that must be placed in a larger envelope or without folding.

When Should I Use First-Class Flats Over First-Class Letters?

First-Class Mail Flats are the best of the types of First-Class Mail when:

• The amount of required content is too large to fit in a letter-size envelope.

• Oversized materials must remain unfolded.

Letters are the less expensive of the types of First-Class Mail, and, thus, many organizations may prefer them over flats. Letters are the best choice when:

• There are few sheets in a mailing, and all sheets can fit inside a letter-size envelope.

• Sheets can be folded in a trifold style without affecting brand presentation.

While they may carry higher postage than letters, flats maintain the service features of all types of First-Class Mail, such as forwarding and return handling. They are suitable for time-sensitive, transactional, and compliance-driven communications.

What Is Automation First-Class Mail?

Automation First-Class Mail is a category for mailpieces prepared according to specific barcode, addressing, and formatting standards. Following these guidelines allows mail to be processed on high-speed sorting equipment. This lets mailings qualify for automation pricing, a reduced-price tier offered by the USPS to incentivize this kind of mail preparation.

What Makes Types of First-Class Mail Automation Eligible?

To qualify for automation pricing, all types of First-Class Mail must meet defined automation mail requirements related to the following factors, among others:

Address Quality

Mailings sent at automation rates must take steps to guarantee address quality. These include:

• CASS-certified address standardization. Mailing lists must be checked with CASS-certified software within 180 days of mailing.

• An address list with the correct zip code, ZIP+4 code, or numeric equivalent to the delivery point barcode for each mailpiece.

IMB

All automation-compatible types of First-Class Mail must have an Intelligent Mail Barcode, or IMB, placed in the address block or in the barcode clear zone.

Machinability

All types of First-Class Mail that are automation-compatible must meet machinability guidelines. Specifically, these mailpieces must, among other requirements:

• Be rectangular in shape.

• Be of uniform thickness, with no creases, folds, tears, protrusions, clasps, or rigid inserts.

• Be flexible.

Minimum Mailing Size

First-Class Mail mailings at automation prices must contain a minimum of 500 mailpieces.