Lob Help Center

Mail piece design formats

All about mail piece design formats for artboards, files, fonts, and images

Anatomy of a mailpiece

When you send an API request to Lob, you are sending 3 pieces of information: 

  1. the "To" address, 
  2. the "From" address, and 
  3. the content.

Below are some best practices to follow when designing content for Lob.

Note: all measurements are in inches, denoted by the double prime symbol (e.g. 4" x 6").

Artboard components

Bleed area

In the above postcard, you'll notice that the file that you are sending to Lob is actually 4.25" x 6.25" instead of 4" x 6". This extra space is what we call the Bleed Area. The Bleed Area is included to ensure that artwork gets printed to the edge. The artwork gets printed with slightly larger dimensions than the actual card and is subsequently trimmed down in production. Backgrounds and graphics should be extended into the Bleed Area. If they don't extend into the Bleed Area, it can result in a white or unprinted border on the edge of the postcard.

There is no need to include crop marks in your submitted content.

Trim zone

The Trim Zone captures the finished size of a mail piece, which will result from the printer trimming down a larger sheet of paper. Artwork that extends into the Bleed Area will be trimmed down to the size of the actual mail piece.

Safe zone

Keep all critical text and artwork within 1/8" from the edge of the final size to ensure no important content is ever trimmed off.

Mail piece size

The sizes of our mail pieces and their respective print layout requirements can be found in each respective section in the Help Center. Note that the API will return an error if you input a non-HTML file with the incorrect dimensions.

No-ink zones

Address block & postage

On our postcards and self-mailer specs, there is a space marked as *RED: INK-FREE AREA* on the backside of the mail piece. Anything in this area will not be printed, as this space is where the postage and address information will be printed during the production process. Address blocks for 4" x 6" postcards measure 2.375" x 3.2835", and all other postcard and self-mailer blocks measure 2.375" x 4.0".

On letters, the address block is 3.15" x 2" large and is located 0.6" from the left edge and 0.84" from the top edge. A white box will be printed, upon which will be printed the address and barcode information. Any content in this area will be covered and will not be visible.  

On checks, the check itself will be printed at the 8.5" x 3.625" area at the top. This area must thus be left blank. Anything printed in this area will not be printed to leave room for check details, including address information, payment amount, signature, and bank routing numbers. All text and important information should be included within the safe zone of the check bottom or check attachment pages.

Eco-conscious certification 

Lob has partnered with USPS to include an eco-conscious certification to help customers demonstrate to their end-recipients that they are sending mail in an environmentally responsible way.

The eco-conscious certification will automatically be included within the official use address block of all mailers that are printed by Lob. This currently applies to postcards and self-mailers, but support of this certification will be expanded to other mail types printed by Lob in the future. It will not impact your workflow or the way you design your creatives in any way.

The certification measures 0.349" x 0.349", is printed in full color, and depending on the mailer size (and address block) of the postcard or self-mailer, will be placed between the return address, postage indicia, and IMb. Address block placement and measurements can be found below.

Placement for 4x6" postcards only
Placement for all other postcards & self-mailers
Address block size (H x W): 2.375" x 3.2835"
  • Distance from right edge of return address: 0.32"
  • Distance from left edge of postage indicia: 0.25"
  • Distance from top edge of IMb code: 0.36"
Address block size (H x W): 2.375" x 4.0"
  • Distance from right edge of return address: 0.88"
  • Distance from left edge of postage indicia: 0.25"
  • Distance from top edge of IMb code: 0.46"

For any questions on our eco-conscious certification, reach out to your CSM or support@lob.com.

QR codes & sequence ID numbers

On letters and checks, there is a small QR code and a set of sequence IDs that will be printed on the bottom left corner during the mail production process, which are used as part of Lob's internal quality control process. These codes get scanned by cameras on our printers to ensure that the correct pages go into each corresponding mail piece as they get inserted into envelopes. They will both appear on each page that contains content, and cannot be removed.

While the red zone around the QR code is 0.5" x 0.5" large, keep a 0.58" x 0.58" sized area at the bottom left corner of the letter clear of any content as it will be covered and obscured by a white box that will be printed around the QR code.   

Sequence IDs itself are 1.45" x 0.09" long, and is located 0.3" from the left edge and 2.2375" from the bottom edge of the page. Any content behind the sequence ID will be covered and obscured by a white box that will be printed to make the ID legible.

Plan your artwork submissions accordingly by avoiding printing any important text or artwork in the area saved for QR code and sequence numbers.

Intelligent Mail barcode

The Intelligent Mail barcode (IMb) is a 65-bar US Postal Service barcode used for mail sorting and tracking. It includes the routing ZIP and tracking information. USPS requires the use of the IMb in order for Lob's mail to benefit from automated processes.

File and font formats


We highly recommend designing your direct mail in HTML, as opposed to static formats. The flexibility afforded by HTML includes the incorporation of dynamic merge variables into the design, which enable sending personalized content at scale. See dynamic personalization for more information.

When designing content with HTML, use inline styles or an internal stylesheet. Do not use an external stylesheet. If you are linking to images, please ensure that they are at least 300 dpi (but there is no need to go higher than 300 dpi). Because the content is only being designed for a single size, we recommend using absolute positioning, as shown below.

body {
  width: 6.25in;
  height: 4.25in;
  margin: 0;
  padding: 0;
  background-image: url(https://s3-us-west-2.amazonaws.com/public.lob.com/assets/beach.jpg);
  background-size: 6.25in 4.25in;
  background-repeat: no-repeat;

#safe-area {
  position: absolute;
  width: 5.875in;
  height: 3.875in;
  left: 0.1875in;
  top: 0.1875in;
  background-color: rgba(255,255,255,0.5);

PDF guidelines

Lob processes and prints various types of PDFs, however the below PDF formatting guidelines will help ensure successful and accurate printing. 

  • All generated PDFs need to be PDF/X-1a compliant
  • Transparencies should be flattened. If transparencies are not flattened, overlapping colors may change and objects may disappear completely
  • Fonts must be outlined (preferred) or embedded. Fonts that have not been outlined or embedded might change or render incorrectly, specific letters may be substituted with incorrect glyphs
  • File size should be under 5MB. Lower file size allows for easier processing at the print level. Large files have a higher potential to fail
  • Color should be CMYK Color Space (SWOP v2 or GRACoL 2006 preferred). By submitting CMYK you will avoid potential conversion errors when Lob changes RGB to CMYK
  • Image resolution should be 300 ppi. If resolution is below 300 ppi, you may see pixelation and incorrect color saturation of your images, if ppi greatly exceeds 300 the file size will be too large and have the potential to fail
  • NO printers marks. Do not submit printer marks (or trim lines) including, but not limited to crop marks, trim marks, bleed marks, slug lines, registration marks, color bars, page information, etc. 

Avoiding printers marks

Lob's APIs will not accept printer marks (or trim lines). Our production facilities have several QA standards in place to ensure cuts are made appropriately and the color is correct. Any content uploaded is treated as part of the design, and thus the printer marks will cause the dimensions to be larger than the intended image size, resulting in an error.

If you are exporting an image for a printing proof the way you usually would when sending images to traditional printers, then the trim lines should be unticked in your settings to ensure a sizing error does not occur. 

To remove these trim lines and color bars from your PDF, open your file in Adobe Acrobat, go to Settings, and clear the Printer’s Marks checkbox.

Avoid having any printer's marks in your PDF by ensuring your image export settings do not include them. 

Note that whether or not you export with “Bleed” will depend on how you built your template. If you already manually added the bleed (e.g. 4.25" x 6.25" artwork), then you should have that unticked as well.

Supported font formats

Ideally, all fonts in provided PDFs should be embedded. Embedding a font in a PDF ensures that the final printed product will look as it was designed. Fonts can vary greatly in size and shape, even within the same family. If the exact font that was used to design the artwork is not used to print, the look and placement of the text is not guaranteed to be the same.

In general, requests that provide PDFs with un-embedded fonts will be rejected. We make an exception for "standard fonts", a set of fonts that we have identified as being common. PDFs that contain un-embedded fonts that are found in the list, and match the accepted font type will be accepted. Otherwise, the request will be rejected.

We support the following web font formats:

  • TTF
  • OTF
  • SVG
  • EOT
  • Google web fonts
  • Custom fonts within your HTML templates
  • See our full list of supported PDF Fonts

We do not support Adobe (Typekit) fonts

  • Adobe Fonts (formerly Typekit Fonts): These fonts require white-listing a specific domain, which Lob is unable to do. Our recommendation is to either host the font yourself and use it within your HTML, or find an appropriate non-Typekit font to replace it with. 
  • Make sure all non-standard fonts must be embedded.

Image formats

When using PNGs or JPEGs with Lob, we require a minimum of 300 dpi. The dpi is calculated as (width of image in pixels) / (width of product in inches) and (length of image in pixels) / (length of product in inches). For example: 1275px x 1875px image used to create a 4.25" x 6.25" postcard has a dpi of 300. It is also recommended that you don't greatly exceed 300 dpi, as this will result in unnecessary additional file size.

Submitted images must have the same length to width ratio as the chosen product. Images will not be cropped or stretched by the API.


This is a raster image format that can have a transparent background. It is generally a higher quality than other image formats.


This is a raster image format that is often used for photographs. It does not allow for a transparent background.

Hosting content

When you pass an image or send HTML in your API request, Lob will then render and host the content. If you are sending at high volumes, we recommend you host the content yourself on a performant file hosting provider, such as Amazon S3, and send Lob a hosting URL to the content in your API request. This will reduce your API request time.

Rendering best practices

To see how your HTML is rendered, create a Test API request either through the API or on the Dashboard. You'll be able to see a PDF proof of exactly what the design looks like. We highly recommend sending yourself a printed piece to validate the mail piece appearance.

Example pieces

See Lob's Template Gallery for pre-designed templates to help you get started. You can fork these to create your own designs.


Lob's HTML renderer is based off of Webkit. For this reason, using the Safari browser will show previews more accurately. For the best results, we recommend submitting test API requests and reviewing the rendered PDF.


We highly recommend using the Adobe Creative Suite (Adobe Illustrator, Photoshop, or InDesign) to design your content. This will give you design flexibility and multiple export options.

Converting from PDF to HTML

We recommend using a developer to convert your PDF designs to HTML. We'd estimate 15 minutes to 2 hours of development time for the average file. Some applications like Adobe Illustrator come with HTML export options, but note that their exports won't typically produce HTML that conforms to Lob's requirements.

Information privacy considerations 

Sensitive PII

Printing and mailing any Sensitive Personally Identifiable Information (Sensitive PII) will be up to the users’ own discretion. See the USPS Marketing Mail Eligibility guidance around how including personal information can also impact postage and mailing class options. If you require any mailings that contain Sensitive PII to be sent, we strongly recommend they be sent as a Letter form factor.


Lob is compliant with the Health Insurance Portability and Accountability Act of 1996 (HIPAA). If you require HIPAA-compliant healthcare mailings that include protected health information (PHI) to be sent, we strongly recommend they be sent as a letter, which is a HIPAA-compliant form factor.

Currently, we do not support HIPAA compliance for self-mailers, postcards, or letter-affixed cards.

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