Direct Mail Sizes: The Ultimate Guide To Mail Dimensions

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If you’re a marketer that is planning a direct mail campaign, you might check out the specs from the US Postal Service for direct mail sizes. You also might get really confused!

The names and the exact specifications for standard direct mail sizes are clearly labeled. They just might not make much common sense.

Here at Postalytics, we allow you to design direct mailer templates in a range of sizes and craft sequences that use a range of different formats to deliver your offer and message to your prospects. However, knowing what type of flyer, postcard or letter to send can be difficult. Even when you choose the type of collateral to send, most formats commonly include multiple sizes. For a detailed look at the rules and regulations for USPS shipping, refer to their Basic Standards for Mailing.

Why is this important? Because if you don’t follow the exact direct mail size for your creative, you can end up having to pay more, lots more, for postage. Google Nonmachinable Letters for some fun reading :-).

You want your direct mail sizes to match the USPS specs to be “machinable” and eligible for “presort” prices. Machinable pieces must be within specific sizes, shapes and weights.

Let’s start with an overview of USPS direct mail terminology.

What Is A Postcard (At least for direct mail purposes)?

USPS Postcard Size Specs

In USPS direct mail speak, a “Postcard” is something very specific. It is a rectangular (not square or any other shape) slip of paper with specific dimensions. USPS Postcards qualify for special postage rates, and are always delivered first class.

The standard direct mail sizes for postcards are:

  • Rectangular, not square
  • Between 3 ½” and 4 ¼” height
  • Between 5” and 6” width
  • Between .007” and .016” Thickness

Postalytics offers a standard USPS postcard that is the maximum size (4 ¼” x 6”). Here’s the specs that you’d hand to a graphic designer:

4x6 postcard direct mail sizes

You can download these specs, along with our full Postalytics Style Guide that overlays into Adobe products:

Is That It For Postcards? Not Really

Most folks (including we at Postalytics) refer to postcards a bit more generally. While we offer the standard 4×6 postcard size (actually 4 ¼” x 6” max sized), we also offer other sizes of what we call postcards.

The problem is that the USPS calls these other postcards “letters”.

What Is A Letter (According to USPS Specs)?

USPS Letter specifications

The USPS direct mail specs refer to letters a bit more generally. The confusing thing is that in their world, a letter doesn’t need to be in an envelope!

The rest of the world considers single page slips of paper with marketing messages on them to be postcards. Postcard marketing is a huge business, and it is not limited to the USPS terminology. Postalytics offers postcards that are 6×9 and 6×11.

That being said, postcards that qualify as USPS “machinable letters” can qualify for special direct mail postage prices. You want your postcards to meet these specs. Those 6×9 and 6×11 postcards that Postalytics mails meet the machinable letter direct mail sizes.

For first class and marketing mail (standard class) machinable letters (enveloped and nonenveloped) must fit these criteria:

  • Rectangular, with four square corners and parallel opposite sides. Letter sized, card-type mailpieces may have finished corners that do not exceed a radius of 1/8th inch.
  • Height between 3 ½” and 6 ⅛”
  • Width between 5” and 11 ½”
  • Thickness between 0.007” and ¼ inch

If your direct mail sizes are outside of these ranges, they’ll fall into the Nonmachinable category & cost you more.

What about Portrait vs Landscape Postcard Direct Mail Sizes?

The specs that you’ve seen so far generally refer to postcards and letters that are rectangular and in “landscape” format. Most postcards and letters are sent that way.

You do not have to use a landscape format. In fact, some of the most successful mailers that we’ve seen have used a Portrait postcard front (across all of our sizes). Portrait sizing really only impacts the orientation of the images and copy on the postcard, not the size of the direct mail.

The Postalytics Build Direct Mail Postcards Offline article has full specs for portrait postcards.

Enveloped Direct Mail Letter Sizes

When dealing with an enveloped direct mail letter, the USPS will measure the envelope itself to see if it meets their direct mail sizing criteria.

The standard, #10 envelope that most businesses use is 4 ⅛” height and 9 ½” width.

Your creative (which gets folded and put in the envelope) is generally sized at 11” height and 8 ½” width. You can have many pages, along as you stay within the thickness limit previously described (¼” max) and the weight limit (3 ½ ounces).

A letter-sized envelope for lead generation campaigns to a house file produced the best response rate, at 15.1%.  (Source: ANA/DMA Response Rate Report 2018) @ANAmarketers

We recently published an article about direct mail sales letters, that fit within these standard direct mail letter sizes and formats.

Sometimes Bigger is Better (and Sometimes Not)

A common trend that we see among new customers that come to us is that they believe that the larger the piece, the more effective and attention-grabbing it is. It’s true, too — a lot of time, anyway. According to the Direct Marketing Association, using an oversized envelope can result in a 5% response rate when mailing to an in-house list.

When you look at it from the customer’s perspective, it makes sense. You’re sifting through the mail for the day. There might be a handful of promotional pieces, each having the familiar signs of “junk mail.” A larger piece of direct mail makes it easy to stand out from the competition and force the reader to give your piece a second look.

For this reason, our 6”x11” postcards are one of the most popular choices in the Postalytics system. They give our customers more real estate at an affordable price and stand out from competitors that use the more common, small postcards.

This isn’t to say that you should never use a smaller direct mail postcard. There are situations (depending on your offer and the amount of real estate your messaging will need) where smaller choices may be more effective. To determine what the best size for your direct mail pieces is, you’ll need to do some testing.

Testing & Analytics

Automated direct mail dashboard

It’s impossible to know which format will provide the best results for your campaign without doing a little testing first. Testing a small sample size with different formats can be a great idea, providing insight into which formats will work best for your campaign.

When you test different formats, try to keep the messaging and offer as consistent as possible to make sure that other factors aren’t affecting the response that you receive. Using Postalytics detailed direct mail analytics which integrates directly into popular customer relationship management systems, you can evaluate the effectiveness of each sample campaign that you send you then identify the campaign and format that provide the most return to your business.